| Message ID | 1461024699-13734-1-git-send-email-ahs3@redhat.com (mailing list archive) |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
+ Ryan Hi Al, On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: > When CPPC is being used by ACPI on arm64, user space tools such as > cpupower report CPU frequency values from sysfs that are incorrect. > > What the driver was doing was reporting the values given by ACPI tables > in whatever scale was used to provide them. However, the ACPI spec > defines the CPPC values as unitless abstract numbers. Internal kernel > structures such as struct perf_cap, in contrast, expect these values > to be in KHz. When these struct values get reported via sysfs, the > user space tools also assume they are in KHz, causing them to report > incorrect values (for example, reporting a CPU frequency of 1MHz when > it should be 1.8GHz). > > While the investigation for a long term fix proceeds (several options > are being explored, some of which may require spec changes or other > much more invasive fixes), this patch forces the values read by CPPC > to be read in KHz, regardless of what they actually represent. > > The downside is that this approach has some assumptions: > > (1) It relies on SMBIOS3 being used, *and* that the Max Frequency > value for a processor is set to a non-zero value. > > (2) It assumes that all processors run at the same speed. This > patch retrieves the first CPU Max Frequency from a type 4 DMI > record that it can find. This may not be an issue, however, as a > sampling of DMI data on x86 and arm64 indicates there is often only > one such record regardless. > > For arm64 servers, this may be sufficient, but it does rely on > firmware values being set correctly. Hence, other approaches are > also being considered. > > This has been tested on three arm64 servers, with and without DMI, with > and without CPPC support. > > Changes for v2: > -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, > not SELECT DMI (found by build daemon) > > Signed-off-by: Al Stone <ahs3@redhat.com> This looks like a good short term solution. Does it make more sense to move this to the cppc_cpufreq driver though? Since that ties more closely into the cpufreq framework which requires the kHz values in sysfs. That way we can keep the cppc_acpi.c shim compliant with the ACPI spec. (i.e. values read in cppc structures remain abstract and unitless). Rafael, Viresh, others, Any other ideas how to handle this better in the long term? - Decouple the cpufreq sysfs from the cppc driver and introduce its own entries. Is it possibly to do this cleanly while still allowing usage of cpufreq registration with existing governors? - Come up with a scaling factor using the PMU cycle counter at boot before the CPPC drivers are initialized. This would use the current freq set by some UEFI var. This would possibly require some messy perfevents plumbing and added bootup time though. - .. ? Cheers, Ashwin. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/19/2016 02:12 PM, Ashwin Chaugule wrote: > + Ryan > > Hi Al, > > On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: >> When CPPC is being used by ACPI on arm64, user space tools such as >> cpupower report CPU frequency values from sysfs that are incorrect. >> >> What the driver was doing was reporting the values given by ACPI tables >> in whatever scale was used to provide them. However, the ACPI spec >> defines the CPPC values as unitless abstract numbers. Internal kernel >> structures such as struct perf_cap, in contrast, expect these values >> to be in KHz. When these struct values get reported via sysfs, the >> user space tools also assume they are in KHz, causing them to report >> incorrect values (for example, reporting a CPU frequency of 1MHz when >> it should be 1.8GHz). >> >> While the investigation for a long term fix proceeds (several options >> are being explored, some of which may require spec changes or other >> much more invasive fixes), this patch forces the values read by CPPC >> to be read in KHz, regardless of what they actually represent. >> >> The downside is that this approach has some assumptions: >> >> (1) It relies on SMBIOS3 being used, *and* that the Max Frequency >> value for a processor is set to a non-zero value. >> >> (2) It assumes that all processors run at the same speed. This >> patch retrieves the first CPU Max Frequency from a type 4 DMI >> record that it can find. This may not be an issue, however, as a >> sampling of DMI data on x86 and arm64 indicates there is often only >> one such record regardless. >> >> For arm64 servers, this may be sufficient, but it does rely on >> firmware values being set correctly. Hence, other approaches are >> also being considered. >> >> This has been tested on three arm64 servers, with and without DMI, with >> and without CPPC support. >> >> Changes for v2: >> -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, >> not SELECT DMI (found by build daemon) >> >> Signed-off-by: Al Stone <ahs3@redhat.com> > > This looks like a good short term solution. Does it make more sense to > move this to the cppc_cpufreq driver though? Since that ties more > closely into the cpufreq framework which requires the kHz values in > sysfs. That way we can keep the cppc_acpi.c shim compliant with the > ACPI spec. (i.e. values read in cppc structures remain abstract and > unitless). Perhaps. Doing it that way made the patch a bit messier since cppc_acpi.c would set values that then had to be replaced in cppc_cpufreq.c, so initialization looked odd to me; that's how I ended up here. You do raise a good point, however; I'll look at that approach again since I could have missed an easier way to do it. > Rafael, Viresh, others, > > Any other ideas how to handle this better in the long term? > > - Decouple the cpufreq sysfs from the cppc driver and introduce its > own entries. Is it possibly to do this cleanly while still allowing > usage of cpufreq registration with existing governors? > > - Come up with a scaling factor using the PMU cycle counter at boot > before the CPPC drivers are initialized. This would use the current > freq set by some UEFI var. This would possibly require some messy > perfevents plumbing and added bootup time though. > > - .. ? > > > Cheers, > Ashwin. > The other thought that occurs to me is to go back through the perf_cap and cpufreq structs and make them more general -- perhaps store the units being used and pointers to functions to convert them to KHz. This may require separating sysfs data for perf_cap from the cpufreq sysfs data from the cppc sysfs data. But, if units are then reported out to sysfs, user space tools can do whatever conversions they want, or at least know what they're reporting instead of there being an implicit ABI between the kernel and the tools. This would be a far more invasive patch set, I think, but it still may be the right thing to do for the long term.
On Tue, Apr 19, 2016 at 1:11 AM, Al Stone <ahs3@redhat.com> wrote: > > When CPPC is being used by ACPI on arm64, user space tools such as > cpupower report CPU frequency values from sysfs that are incorrect. > > What the driver was doing was reporting the values given by ACPI tables > in whatever scale was used to provide them. However, the ACPI spec > defines the CPPC values as unitless abstract numbers. Internal kernel > structures such as struct perf_cap, in contrast, expect these values > to be in KHz. When these struct values get reported via sysfs, the > user space tools also assume they are in KHz, causing them to report > incorrect values (for example, reporting a CPU frequency of 1MHz when > it should be 1.8GHz). > > While the investigation for a long term fix proceeds (several options > are being explored, some of which may require spec changes or other > much more invasive fixes), this patch forces the values read by CPPC > to be read in KHz, regardless of what they actually represent. > > The downside is that this approach has some assumptions: > > (1) It relies on SMBIOS3 being used, *and* that the Max Frequency > value for a processor is set to a non-zero value. > > (2) It assumes that all processors run at the same speed. This Sometimes short-term solution becomes long-term. It's worth to place comment in code about this assumption. > patch retrieves the first CPU Max Frequency from a type 4 DMI > record that it can find. This may not be an issue, however, as a > sampling of DMI data on x86 and arm64 indicates there is often only > one such record regardless. > > For arm64 servers, this may be sufficient, but it does rely on > firmware values being set correctly. Hence, other approaches are > also being considered. > > This has been tested on three arm64 servers, with and without DMI, with > and without CPPC support. > > Changes for v2: > -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, > not SELECT DMI (found by build daemon) > > Signed-off-by: Al Stone <ahs3@redhat.com> > --- > drivers/acpi/cppc_acpi.c | 61 +++++++++++++++++++++++++++++++++++++++++---- > drivers/cpufreq/Kconfig.arm | 1 + > 2 files changed, 57 insertions(+), 5 deletions(-) > > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c > index 8adac69..d61ced6 100644 > --- a/drivers/acpi/cppc_acpi.c > +++ b/drivers/acpi/cppc_acpi.c > @@ -40,6 +40,9 @@ > #include <linux/cpufreq.h> > #include <linux/delay.h> > #include <linux/ktime.h> > +#include <linux/dmi.h> > + > +#include <asm/unaligned.h> > > #include <acpi/cppc_acpi.h> > /* > @@ -709,6 +712,47 @@ static int cpc_write(struct cpc_reg *reg, u64 val) > return ret_val; > } > > +static u64 cppc_dmi_khz; > + > +static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private) > +{ > + u16 *mhz = (u16 *)private; > + const u8 *dmi_data = (const u8 *)dm; > + > + if (dm->type == DMI_ENTRY_PROCESSOR && dm->length >= 48) > + *mhz = (u16)get_unaligned((const u16 *)(dmi_data + 0x14)); > +} > + > + > +static u64 cppc_get_dmi_khz(void) > +{ > + u16 mhz; > + > + dmi_walk(cppc_find_dmi_mhz, &mhz); > + > + /* > + * Real stupid fallback value, just in case there is no > + * actual value set. > + */ > + mhz = mhz ? mhz : 1; > + > + return (1000 * mhz); > +} > + > +static u64 cppc_unitless_to_khz(u64 min, u64 max, u64 val) > +{ > + /* > + * The incoming val should be min <= val <= max. Our > + * job is to convert that to KHz so it can be properly > + * reported to user space via cpufreq_policy. > + */ > + > + if (!cppc_dmi_khz) > + cppc_dmi_khz = cppc_get_dmi_khz(); > + > + return ((val - min) * cppc_dmi_khz) / (max - min); How pedantic should the kernel be while dealing with this values? This 1) can potentially divide by zero (extra care is required to perform this in Solar System) and 2) can return 0. Not sure if there is some benefit for firmware to export such values. [..] Best regards, Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/21/2016 08:53 AM, Alexey Klimov wrote: > > On Tue, Apr 19, 2016 at 1:11 AM, Al Stone <ahs3@redhat.com> wrote: >> >> When CPPC is being used by ACPI on arm64, user space tools such as >> cpupower report CPU frequency values from sysfs that are incorrect. >> >> What the driver was doing was reporting the values given by ACPI tables >> in whatever scale was used to provide them. However, the ACPI spec >> defines the CPPC values as unitless abstract numbers. Internal kernel >> structures such as struct perf_cap, in contrast, expect these values >> to be in KHz. When these struct values get reported via sysfs, the >> user space tools also assume they are in KHz, causing them to report >> incorrect values (for example, reporting a CPU frequency of 1MHz when >> it should be 1.8GHz). >> >> While the investigation for a long term fix proceeds (several options >> are being explored, some of which may require spec changes or other >> much more invasive fixes), this patch forces the values read by CPPC >> to be read in KHz, regardless of what they actually represent. >> >> The downside is that this approach has some assumptions: >> >> (1) It relies on SMBIOS3 being used, *and* that the Max Frequency >> value for a processor is set to a non-zero value. >> >> (2) It assumes that all processors run at the same speed. This > > Sometimes short-term solution becomes long-term. It's worth to place > comment in code about this assumption. True. I'll add a comment. Thanks. >> patch retrieves the first CPU Max Frequency from a type 4 DMI >> record that it can find. This may not be an issue, however, as a >> sampling of DMI data on x86 and arm64 indicates there is often only >> one such record regardless. >> >> For arm64 servers, this may be sufficient, but it does rely on >> firmware values being set correctly. Hence, other approaches are >> also being considered. >> >> This has been tested on three arm64 servers, with and without DMI, with >> and without CPPC support. >> >> Changes for v2: >> -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, >> not SELECT DMI (found by build daemon) >> >> Signed-off-by: Al Stone <ahs3@redhat.com> >> --- >> drivers/acpi/cppc_acpi.c | 61 +++++++++++++++++++++++++++++++++++++++++---- >> drivers/cpufreq/Kconfig.arm | 1 + >> 2 files changed, 57 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c >> index 8adac69..d61ced6 100644 >> --- a/drivers/acpi/cppc_acpi.c >> +++ b/drivers/acpi/cppc_acpi.c >> @@ -40,6 +40,9 @@ >> #include <linux/cpufreq.h> >> #include <linux/delay.h> >> #include <linux/ktime.h> >> +#include <linux/dmi.h> >> + >> +#include <asm/unaligned.h> >> >> #include <acpi/cppc_acpi.h> >> /* >> @@ -709,6 +712,47 @@ static int cpc_write(struct cpc_reg *reg, u64 val) >> return ret_val; >> } >> >> +static u64 cppc_dmi_khz; >> + >> +static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private) >> +{ >> + u16 *mhz = (u16 *)private; >> + const u8 *dmi_data = (const u8 *)dm; >> + >> + if (dm->type == DMI_ENTRY_PROCESSOR && dm->length >= 48) >> + *mhz = (u16)get_unaligned((const u16 *)(dmi_data + 0x14)); >> +} >> + >> + >> +static u64 cppc_get_dmi_khz(void) >> +{ >> + u16 mhz; >> + >> + dmi_walk(cppc_find_dmi_mhz, &mhz); >> + >> + /* >> + * Real stupid fallback value, just in case there is no >> + * actual value set. >> + */ >> + mhz = mhz ? mhz : 1; >> + >> + return (1000 * mhz); >> +} >> + >> +static u64 cppc_unitless_to_khz(u64 min, u64 max, u64 val) >> +{ >> + /* >> + * The incoming val should be min <= val <= max. Our >> + * job is to convert that to KHz so it can be properly >> + * reported to user space via cpufreq_policy. >> + */ >> + >> + if (!cppc_dmi_khz) >> + cppc_dmi_khz = cppc_get_dmi_khz(); >> + >> + return ((val - min) * cppc_dmi_khz) / (max - min); > > How pedantic should the kernel be while dealing with this values? I'm not sure it can be. By definition, the CPPC values define an abstract range. We are only associating it with a frequency here because those are the units assumed elsewhere in the kernel, and that user space tools make the same assumptions. What I'm looking at for the longer term is possibly breaking those assumptions so that maybe we can be pedantic. > This 1) can potentially divide by zero (extra care is required to > perform this in Solar System) and 2) can return 0. Hrm. I'll double check the path for divide by zero; I thought that was covered elsewhere along the path but I might have missed it. A zero in this case would mean the processor is running at its lowest possible level of performance, and is an artifact of mapping the CPPC abstract value onto a linear scale from 0 to max KHz. Granted, that may not be exactly the same as 0 KHz; I'm open to suggestions here. If there's a relatively straightforward way to get a processor's minimum operating frequency (apart from completely off), we could eliminate the zero. > Not sure if there is some benefit for firmware to export such > values. Reporting a divide by zero would be bad and should not happen; a value of zero, though, could be argued. Since we're using a linear scale from zero to max KHz, it's not unexpected. That being said, though, the only reason for this patch is so that user space does not report completely incorrect values; we were seeing MHz values reported by cpupower when they should have been GHz, for example.
On 19-04-16, 16:12, Ashwin Chaugule wrote: > + Ryan > > Hi Al, > > On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: > > When CPPC is being used by ACPI on arm64, user space tools such as > > cpupower report CPU frequency values from sysfs that are incorrect. > > > > What the driver was doing was reporting the values given by ACPI tables > > in whatever scale was used to provide them. However, the ACPI spec > > defines the CPPC values as unitless abstract numbers. Internal kernel > > structures such as struct perf_cap, in contrast, expect these values > > to be in KHz. When these struct values get reported via sysfs, the > > user space tools also assume they are in KHz, causing them to report > > incorrect values (for example, reporting a CPU frequency of 1MHz when > > it should be 1.8GHz). > > > > While the investigation for a long term fix proceeds (several options > > are being explored, some of which may require spec changes or other > > much more invasive fixes), this patch forces the values read by CPPC > > to be read in KHz, regardless of what they actually represent. > > > > The downside is that this approach has some assumptions: > > > > (1) It relies on SMBIOS3 being used, *and* that the Max Frequency > > value for a processor is set to a non-zero value. > > > > (2) It assumes that all processors run at the same speed. This > > patch retrieves the first CPU Max Frequency from a type 4 DMI > > record that it can find. This may not be an issue, however, as a > > sampling of DMI data on x86 and arm64 indicates there is often only > > one such record regardless. Don't we have any big LITTLE ARM servers yet ? Or we will not have them at all ? > > For arm64 servers, this may be sufficient, but it does rely on > > firmware values being set correctly. Hence, other approaches are > > also being considered. > > > > This has been tested on three arm64 servers, with and without DMI, with > > and without CPPC support. > > > > Changes for v2: > > -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, > > not SELECT DMI (found by build daemon) > > > > Signed-off-by: Al Stone <ahs3@redhat.com> > > This looks like a good short term solution. Does it make more sense to > move this to the cppc_cpufreq driver though? Since that ties more > closely into the cpufreq framework which requires the kHz values in > sysfs. That way we can keep the cppc_acpi.c shim compliant with the > ACPI spec. (i.e. values read in cppc structures remain abstract and > unitless). > > Rafael, Viresh, others, > > Any other ideas how to handle this better in the long term? > > - Decouple the cpufreq sysfs from the cppc driver and introduce its > own entries. Is it possibly to do this cleanly while still allowing > usage of cpufreq registration with existing governors? > > - Come up with a scaling factor using the PMU cycle counter at boot > before the CPPC drivers are initialized. This would use the current > freq set by some UEFI var. This would possibly require some messy > perfevents plumbing and added bootup time though. I may be missing the obvious, but can't we just create the cpufreq-table from this table in khz? We wouldn't require any further change then.
On Friday, April 22, 2016 11:00:20 AM Viresh Kumar wrote: > On 19-04-16, 16:12, Ashwin Chaugule wrote: > > + Ryan > > > > Hi Al, > > > > On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: > > > When CPPC is being used by ACPI on arm64, user space tools such as > > > cpupower report CPU frequency values from sysfs that are incorrect. > > > > > > What the driver was doing was reporting the values given by ACPI tables > > > in whatever scale was used to provide them. However, the ACPI spec > > > defines the CPPC values as unitless abstract numbers. Internal kernel > > > structures such as struct perf_cap, in contrast, expect these values > > > to be in KHz. When these struct values get reported via sysfs, the > > > user space tools also assume they are in KHz, causing them to report > > > incorrect values (for example, reporting a CPU frequency of 1MHz when > > > it should be 1.8GHz). > > > > > > While the investigation for a long term fix proceeds (several options > > > are being explored, some of which may require spec changes or other > > > much more invasive fixes), this patch forces the values read by CPPC > > > to be read in KHz, regardless of what they actually represent. > > > > > > The downside is that this approach has some assumptions: > > > > > > (1) It relies on SMBIOS3 being used, *and* that the Max Frequency > > > value for a processor is set to a non-zero value. > > > > > > (2) It assumes that all processors run at the same speed. This > > > patch retrieves the first CPU Max Frequency from a type 4 DMI > > > record that it can find. This may not be an issue, however, as a > > > sampling of DMI data on x86 and arm64 indicates there is often only > > > one such record regardless. > > Don't we have any big LITTLE ARM servers yet ? Or we will not have them at all ? > > > > For arm64 servers, this may be sufficient, but it does rely on > > > firmware values being set correctly. Hence, other approaches are > > > also being considered. > > > > > > This has been tested on three arm64 servers, with and without DMI, with > > > and without CPPC support. > > > > > > Changes for v2: > > > -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, > > > not SELECT DMI (found by build daemon) > > > > > > Signed-off-by: Al Stone <ahs3@redhat.com> > > > > This looks like a good short term solution. Does it make more sense to > > move this to the cppc_cpufreq driver though? Since that ties more > > closely into the cpufreq framework which requires the kHz values in > > sysfs. That way we can keep the cppc_acpi.c shim compliant with the > > ACPI spec. (i.e. values read in cppc structures remain abstract and > > unitless). > > > > Rafael, Viresh, others, > > > > Any other ideas how to handle this better in the long term? > > > > - Decouple the cpufreq sysfs from the cppc driver and introduce its > > own entries. Is it possibly to do this cleanly while still allowing > > usage of cpufreq registration with existing governors? > > > > - Come up with a scaling factor using the PMU cycle counter at boot > > before the CPPC drivers are initialized. This would use the current > > freq set by some UEFI var. This would possibly require some messy > > perfevents plumbing and added bootup time though. > > I may be missing the obvious, but can't we just create the cpufreq-table from > this table in khz? We wouldn't require any further change then. I wouldn't really like to do that, because the freq table would be totally artificial then. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tuesday, April 19, 2016 04:12:41 PM Ashwin Chaugule wrote: > + Ryan > > Hi Al, > > On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: > > When CPPC is being used by ACPI on arm64, user space tools such as > > cpupower report CPU frequency values from sysfs that are incorrect. > > > > What the driver was doing was reporting the values given by ACPI tables > > in whatever scale was used to provide them. However, the ACPI spec > > defines the CPPC values as unitless abstract numbers. Internal kernel > > structures such as struct perf_cap, in contrast, expect these values > > to be in KHz. When these struct values get reported via sysfs, the > > user space tools also assume they are in KHz, causing them to report > > incorrect values (for example, reporting a CPU frequency of 1MHz when > > it should be 1.8GHz). > > > > While the investigation for a long term fix proceeds (several options > > are being explored, some of which may require spec changes or other > > much more invasive fixes), this patch forces the values read by CPPC > > to be read in KHz, regardless of what they actually represent. > > > > The downside is that this approach has some assumptions: > > > > (1) It relies on SMBIOS3 being used, *and* that the Max Frequency > > value for a processor is set to a non-zero value. > > > > (2) It assumes that all processors run at the same speed. This > > patch retrieves the first CPU Max Frequency from a type 4 DMI > > record that it can find. This may not be an issue, however, as a > > sampling of DMI data on x86 and arm64 indicates there is often only > > one such record regardless. > > > > For arm64 servers, this may be sufficient, but it does rely on > > firmware values being set correctly. Hence, other approaches are > > also being considered. > > > > This has been tested on three arm64 servers, with and without DMI, with > > and without CPPC support. > > > > Changes for v2: > > -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, > > not SELECT DMI (found by build daemon) > > > > Signed-off-by: Al Stone <ahs3@redhat.com> > > This looks like a good short term solution. Does it make more sense to > move this to the cppc_cpufreq driver though? Since that ties more > closely into the cpufreq framework which requires the kHz values in > sysfs. That way we can keep the cppc_acpi.c shim compliant with the > ACPI spec. (i.e. values read in cppc structures remain abstract and > unitless). > > Rafael, Viresh, others, > > Any other ideas how to handle this better in the long term? > > - Decouple the cpufreq sysfs from the cppc driver and introduce its > own entries. Is it possibly to do this cleanly while still allowing > usage of cpufreq registration with existing governors? > > - Come up with a scaling factor using the PMU cycle counter at boot > before the CPPC drivers are initialized. This would use the current > freq set by some UEFI var. This would possibly require some messy > perfevents plumbing and added bootup time though. > > - .. ? Not sure at the moment. Plus, there's one more thing to consider. We may end up having to use CPPC on x86 after all (for reasons that are not relevant here), in which case it probably would make sense to merge the acpi-cpufreq and cppc-cpufreq drivers IMO. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2016-04-19 18:53, Al Stone wrote: > On 04/19/2016 02:12 PM, Ashwin Chaugule wrote: >> + Ryan >> >> Hi Al, >> >> On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: >>> When CPPC is being used by ACPI on arm64, user space tools such as >>> cpupower report CPU frequency values from sysfs that are incorrect. >>> >>> What the driver was doing was reporting the values given by ACPI >>> tables >>> in whatever scale was used to provide them. However, the ACPI spec >>> defines the CPPC values as unitless abstract numbers. Internal >>> kernel >>> structures such as struct perf_cap, in contrast, expect these values >>> to be in KHz. When these struct values get reported via sysfs, the >>> user space tools also assume they are in KHz, causing them to report >>> incorrect values (for example, reporting a CPU frequency of 1MHz when >>> it should be 1.8GHz). >>> >>> While the investigation for a long term fix proceeds (several options >>> are being explored, some of which may require spec changes or other >>> much more invasive fixes), this patch forces the values read by CPPC >>> to be read in KHz, regardless of what they actually represent. >>> >>> The downside is that this approach has some assumptions: >>> >>> (1) It relies on SMBIOS3 being used, *and* that the Max Frequency >>> value for a processor is set to a non-zero value. >>> >>> (2) It assumes that all processors run at the same speed. This >>> patch retrieves the first CPU Max Frequency from a type 4 DMI >>> record that it can find. This may not be an issue, however, as a >>> sampling of DMI data on x86 and arm64 indicates there is often >>> only >>> one such record regardless. >>> >>> For arm64 servers, this may be sufficient, but it does rely on >>> firmware values being set correctly. Hence, other approaches are >>> also being considered. >>> >>> This has been tested on three arm64 servers, with and without DMI, >>> with >>> and without CPPC support. >>> >>> Changes for v2: >>> -- Corrected thinko: needed to have DEPENDS on DMI in >>> Kconfig.arm, >>> not SELECT DMI (found by build daemon) >>> >>> Signed-off-by: Al Stone <ahs3@redhat.com> >> >> This looks like a good short term solution. Does it make more sense to >> move this to the cppc_cpufreq driver though? Since that ties more >> closely into the cpufreq framework which requires the kHz values in >> sysfs. That way we can keep the cppc_acpi.c shim compliant with the >> ACPI spec. (i.e. values read in cppc structures remain abstract and >> unitless). > > Perhaps. Doing it that way made the patch a bit messier since > cppc_acpi.c would set values that then had to be replaced in > cppc_cpufreq.c, so initialization looked odd to me; that's how > I ended up here. You do raise a good point, however; I'll look > at that approach again since I could have missed an easier way > to do it. > >> Rafael, Viresh, others, >> >> Any other ideas how to handle this better in the long term? >> >> - Decouple the cpufreq sysfs from the cppc driver and introduce its >> own entries. Is it possibly to do this cleanly while still allowing >> usage of cpufreq registration with existing governors? >> >> - Come up with a scaling factor using the PMU cycle counter at boot >> before the CPPC drivers are initialized. This would use the current >> freq set by some UEFI var. This would possibly require some messy >> perfevents plumbing and added bootup time though. >> >> - .. ? >> >> >> Cheers, >> Ashwin. >> > > The other thought that occurs to me is to go back through the > perf_cap and cpufreq structs and make them more general -- perhaps > store the units being used and pointers to functions to convert them > to KHz. This may require separating sysfs data for perf_cap from the > cpufreq sysfs data from the cppc sysfs data. But, if units are then > reported out to sysfs, user space tools can do whatever conversions > they want, or at least know what they're reporting instead of there > being an implicit ABI between the kernel and the tools. This would > be a far more invasive patch set, I think, but it still may be the > right thing to do for the long term. The issue is a little more fundamental than that even. We are retrofitting a performance management interface (CPPC) into a frequency management framework (cpufreq) and accompanying tools. Regardless of what scheme we come up with for deriving/exposing frequency, we still haven’t completely solved the problem as that assumes a linear relationship between freq and performance. This will work for many but not necessarily all CPPC systems. In fact, making that assumption is explicitly forbidden in the ACPI spec: "OSPM must make no assumption about the exact meaning of the performance values presented by the platform, or how they may correlate to specific hardware metrics like processor frequency." So to be completely consistent with the current spec, we would need to ween the tools off of frequency altogether and move to abstract performance - either specifically when CPPC driver is loaded or more generally. If we think reporting frequency is required that might still be doable, but would need to be separate interface from the CPPC perf scale. But I agree with Al that is a more invasive change. For the time being, I don't think it is unreasonable to assume performance is linear with frequency and come up with a scaling factor via one of several mechanisms: 1) SMBIOS as Al proposed (caveats above) 2) Measure at boot using PMU or other mechanism as Ashwin floated (more complicated but removes dependency on SMBIOS and assumption that freq scale is same across all CPUs) 3) Just hardcode a CPPC perf to kHz mapping - maybe everyone is using MHz today? (simplest but obviously least flexible) 4) Others? None of these are full solution - it is a question of how many different scenarios do we need to cover with initial solution. I think the SMBIOS one is probably a good simplicity/flexibility compromise. -Ryan Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/21/2016 11:30 PM, Viresh Kumar wrote: > On 19-04-16, 16:12, Ashwin Chaugule wrote: >> + Ryan >> >> Hi Al, >> >> On 18 April 2016 at 20:11, Al Stone <ahs3@redhat.com> wrote: >>> When CPPC is being used by ACPI on arm64, user space tools such as >>> cpupower report CPU frequency values from sysfs that are incorrect. >>> >>> What the driver was doing was reporting the values given by ACPI tables >>> in whatever scale was used to provide them. However, the ACPI spec >>> defines the CPPC values as unitless abstract numbers. Internal kernel >>> structures such as struct perf_cap, in contrast, expect these values >>> to be in KHz. When these struct values get reported via sysfs, the >>> user space tools also assume they are in KHz, causing them to report >>> incorrect values (for example, reporting a CPU frequency of 1MHz when >>> it should be 1.8GHz). >>> >>> While the investigation for a long term fix proceeds (several options >>> are being explored, some of which may require spec changes or other >>> much more invasive fixes), this patch forces the values read by CPPC >>> to be read in KHz, regardless of what they actually represent. >>> >>> The downside is that this approach has some assumptions: >>> >>> (1) It relies on SMBIOS3 being used, *and* that the Max Frequency >>> value for a processor is set to a non-zero value. >>> >>> (2) It assumes that all processors run at the same speed. This >>> patch retrieves the first CPU Max Frequency from a type 4 DMI >>> record that it can find. This may not be an issue, however, as a >>> sampling of DMI data on x86 and arm64 indicates there is often only >>> one such record regardless. > > Don't we have any big LITTLE ARM servers yet ? Or we will not have them at all ? My apologies, but I missed this question earlier and just now noticed it. AFAIK, there are no big.LITTLE ARM servers yet. That doesn't mean there aren't any, or that no one is planning one; I just don't know of any. I have been in discussions about doing that, but in the past those have ended up concluding that there is probably no need for that level of power management in a server.
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index 8adac69..d61ced6 100644 --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -40,6 +40,9 @@ #include <linux/cpufreq.h> #include <linux/delay.h> #include <linux/ktime.h> +#include <linux/dmi.h> + +#include <asm/unaligned.h> #include <acpi/cppc_acpi.h> /* @@ -709,6 +712,47 @@ static int cpc_write(struct cpc_reg *reg, u64 val) return ret_val; } +static u64 cppc_dmi_khz; + +static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private) +{ + u16 *mhz = (u16 *)private; + const u8 *dmi_data = (const u8 *)dm; + + if (dm->type == DMI_ENTRY_PROCESSOR && dm->length >= 48) + *mhz = (u16)get_unaligned((const u16 *)(dmi_data + 0x14)); +} + + +static u64 cppc_get_dmi_khz(void) +{ + u16 mhz; + + dmi_walk(cppc_find_dmi_mhz, &mhz); + + /* + * Real stupid fallback value, just in case there is no + * actual value set. + */ + mhz = mhz ? mhz : 1; + + return (1000 * mhz); +} + +static u64 cppc_unitless_to_khz(u64 min, u64 max, u64 val) +{ + /* + * The incoming val should be min <= val <= max. Our + * job is to convert that to KHz so it can be properly + * reported to user space via cpufreq_policy. + */ + + if (!cppc_dmi_khz) + cppc_dmi_khz = cppc_get_dmi_khz(); + + return ((val - min) * cppc_dmi_khz) / (max - min); +} + /** * cppc_get_perf_caps - Get a CPUs performance capabilities. * @cpunum: CPU from which to get capabilities info. @@ -748,17 +792,24 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps) } } + /* + * Since these values in perf_caps will be used in setting + * up the cpufreq policy, they must always be stored in units + * of KHz. If they are not, user space tools will become very + * confused since they assume these are in KHz when reading + * sysfs. + */ cpc_read(&highest_reg->cpc_entry.reg, &high); - perf_caps->highest_perf = high; - cpc_read(&lowest_reg->cpc_entry.reg, &low); - perf_caps->lowest_perf = low; + + perf_caps->highest_perf = cppc_unitless_to_khz(low, high, high); + perf_caps->lowest_perf = cppc_unitless_to_khz(low, high, low); cpc_read(&ref_perf->cpc_entry.reg, &ref); - perf_caps->reference_perf = ref; + perf_caps->reference_perf = cppc_unitless_to_khz(low, high, ref); cpc_read(&nom_perf->cpc_entry.reg, &nom); - perf_caps->nominal_perf = nom; + perf_caps->nominal_perf = cppc_unitless_to_khz(low, high, nom); if (!ref) perf_caps->reference_perf = perf_caps->nominal_perf; diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm index 14b1f93..5555d79 100644 --- a/drivers/cpufreq/Kconfig.arm +++ b/drivers/cpufreq/Kconfig.arm @@ -254,6 +254,7 @@ config ARM_PXA2xx_CPUFREQ config ACPI_CPPC_CPUFREQ tristate "CPUFreq driver based on the ACPI CPPC spec" depends on ACPI + depends on DMI select ACPI_CPPC_LIB default n help
When CPPC is being used by ACPI on arm64, user space tools such as cpupower report CPU frequency values from sysfs that are incorrect. What the driver was doing was reporting the values given by ACPI tables in whatever scale was used to provide them. However, the ACPI spec defines the CPPC values as unitless abstract numbers. Internal kernel structures such as struct perf_cap, in contrast, expect these values to be in KHz. When these struct values get reported via sysfs, the user space tools also assume they are in KHz, causing them to report incorrect values (for example, reporting a CPU frequency of 1MHz when it should be 1.8GHz). While the investigation for a long term fix proceeds (several options are being explored, some of which may require spec changes or other much more invasive fixes), this patch forces the values read by CPPC to be read in KHz, regardless of what they actually represent. The downside is that this approach has some assumptions: (1) It relies on SMBIOS3 being used, *and* that the Max Frequency value for a processor is set to a non-zero value. (2) It assumes that all processors run at the same speed. This patch retrieves the first CPU Max Frequency from a type 4 DMI record that it can find. This may not be an issue, however, as a sampling of DMI data on x86 and arm64 indicates there is often only one such record regardless. For arm64 servers, this may be sufficient, but it does rely on firmware values being set correctly. Hence, other approaches are also being considered. This has been tested on three arm64 servers, with and without DMI, with and without CPPC support. Changes for v2: -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, not SELECT DMI (found by build daemon) Signed-off-by: Al Stone <ahs3@redhat.com> --- drivers/acpi/cppc_acpi.c | 61 +++++++++++++++++++++++++++++++++++++++++---- drivers/cpufreq/Kconfig.arm | 1 + 2 files changed, 57 insertions(+), 5 deletions(-)