| Message ID | 20161028021430.2177-11-robert@sixbynine.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 2016-10-27 at 19:14 -0700, Robert Bragg wrote: > The minimal sampling period is now configurable via a > dev.i915.oa_min_timer_exponent sysctl parameter. > > Following the precedent set by perf, the default is the minimum that > won't (on its own) exceed the default kernel.perf_event_max_sample_rate > default of 100000 samples/s. > > Signed-off-by: Robert Bragg <robert@sixbynine.org> > Reviewed-by: Matthew Auld <matthew.auld@intel.com> > --- > drivers/gpu/drm/i915/i915_perf.c | 42 ++++++++++++++++++++++++++++------------ > 1 file changed, 30 insertions(+), 12 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c > index 4e42073..e3c6f51 100644 > --- a/drivers/gpu/drm/i915/i915_perf.c > +++ b/drivers/gpu/drm/i915/i915_perf.c > @@ -82,6 +82,22 @@ static u32 i915_perf_stream_paranoid = true; > #define INVALID_CTX_ID 0xffffffff > > > +/* for sysctl proc_dointvec_minmax of i915_oa_min_timer_exponent */ > +static int oa_exponent_max = OA_EXPONENT_MAX; > + > +/* Theoretically we can program the OA unit to sample every 160ns but don't > + * allow that by default unless root... > + * > + * The period is derived from the exponent as: > + * > + * period = 80ns * 2^(exponent + 1) > + * > + * Referring to perf's kernel.perf_event_max_sample_rate for a precedent > + * (100000 by default); with an OA exponent of 6 we get a period of 10.240 > + * microseconds - just under 100000Hz > + */ > +static u32 i915_oa_min_timer_exponent = 6; For HSW, the timestamp period is 80ns, so the exponent of 6 translates to sampling rate of ~100000Hz. But the timestamp period may change for other platforms, leading to different values of oa_min_timer_exponent corresponding to sampling rate of ~100000Hz. Do we plan to have this value platform specific subsequently, or the guidance value of ~100000Hz min sampling rate needn't be strictly followed? > + > /* XXX: beware if future OA HW adds new report formats that the current > * code assumes all reports have a power-of-two size and ~(size - 1) can > * be used as a mask to align the OA tail pointer. > @@ -1353,21 +1369,14 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv, > return -EINVAL; > } > > - /* NB: The exponent represents a period as follows: > - * > - * 80ns * 2^(period_exponent + 1) > - * > - * Theoretically we can program the OA unit to sample > + /* Theoretically we can program the OA unit to sample > * every 160ns but don't allow that by default unless > * root. > - * > - * Referring to perf's > - * kernel.perf_event_max_sample_rate for a precedent > - * (100000 by default); with an OA exponent of 6 we get > - * a period of 10.240 microseconds -just under 100000Hz > */ > - if (value < 6 && !capable(CAP_SYS_ADMIN)) { > - DRM_ERROR("Minimum OA sampling exponent is 6 without root privileges\n"); > + if (value < i915_oa_min_timer_exponent && > + !capable(CAP_SYS_ADMIN)) { > + DRM_ERROR("Minimum OA sampling exponent (sysctl dev.i915.oa_min_timer_exponent) is %u without root privileges\n", > + i915_oa_min_timer_exponent); > return -EACCES; > } > > @@ -1475,6 +1484,15 @@ static struct ctl_table oa_table[] = { > .extra1 = &zero, > .extra2 = &one, > }, > + { > + .procname = "oa_min_timer_exponent", > + .data = &i915_oa_min_timer_exponent, > + .maxlen = sizeof(i915_oa_min_timer_exponent), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = &zero, > + .extra2 = &oa_exponent_max, > + }, > {} > }; >
On Wed, Nov 2, 2016 at 6:29 AM, sourab gupta <sourab.gupta@intel.com> wrote: > On Thu, 2016-10-27 at 19:14 -0700, Robert Bragg wrote: > > The minimal sampling period is now configurable via a > > dev.i915.oa_min_timer_exponent sysctl parameter. > > > > Following the precedent set by perf, the default is the minimum that > > won't (on its own) exceed the default kernel.perf_event_max_sample_rate > > default of 100000 samples/s. > > > > Signed-off-by: Robert Bragg <robert@sixbynine.org> > > Reviewed-by: Matthew Auld <matthew.auld@intel.com> > > --- > > drivers/gpu/drm/i915/i915_perf.c | 42 ++++++++++++++++++++++++++++-- > ---------- > > 1 file changed, 30 insertions(+), 12 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_perf.c > b/drivers/gpu/drm/i915/i915_perf.c > > index 4e42073..e3c6f51 100644 > > --- a/drivers/gpu/drm/i915/i915_perf.c > > +++ b/drivers/gpu/drm/i915/i915_perf.c > > @@ -82,6 +82,22 @@ static u32 i915_perf_stream_paranoid = true; > > #define INVALID_CTX_ID 0xffffffff > > > > > > +/* for sysctl proc_dointvec_minmax of i915_oa_min_timer_exponent */ > > +static int oa_exponent_max = OA_EXPONENT_MAX; > > + > > +/* Theoretically we can program the OA unit to sample every 160ns but > don't > > + * allow that by default unless root... > > + * > > + * The period is derived from the exponent as: > > + * > > + * period = 80ns * 2^(exponent + 1) > > + * > > + * Referring to perf's kernel.perf_event_max_sample_rate for a > precedent > > + * (100000 by default); with an OA exponent of 6 we get a period of > 10.240 > > + * microseconds - just under 100000Hz > > + */ > > +static u32 i915_oa_min_timer_exponent = 6; > > For HSW, the timestamp period is 80ns, so the exponent of 6 translates > to sampling rate of ~100000Hz. But the timestamp period may change for > other platforms, leading to different values of oa_min_timer_exponent > corresponding to sampling rate of ~100000Hz. Do we plan to have this > value platform specific subsequently, or the guidance value of ~100000Hz > min sampling rate needn't be strictly followed? > actually it's bothered me a bit that I've been lazy with not having this adapt for gen9+ in later patches I think it would probably be better to make this a Hz based threshold for userspace, otherwise any userspace policy here needs to be adapted for each system with a different timestamp frequency which isn't great. I've updated the patch locally to make this an oa_max_sample_rate parameter in Hz, which I'll aim to test on haswell tomorrow and send out. Thanks, - Robert
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index 4e42073..e3c6f51 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -82,6 +82,22 @@ static u32 i915_perf_stream_paranoid = true; #define INVALID_CTX_ID 0xffffffff +/* for sysctl proc_dointvec_minmax of i915_oa_min_timer_exponent */ +static int oa_exponent_max = OA_EXPONENT_MAX; + +/* Theoretically we can program the OA unit to sample every 160ns but don't + * allow that by default unless root... + * + * The period is derived from the exponent as: + * + * period = 80ns * 2^(exponent + 1) + * + * Referring to perf's kernel.perf_event_max_sample_rate for a precedent + * (100000 by default); with an OA exponent of 6 we get a period of 10.240 + * microseconds - just under 100000Hz + */ +static u32 i915_oa_min_timer_exponent = 6; + /* XXX: beware if future OA HW adds new report formats that the current * code assumes all reports have a power-of-two size and ~(size - 1) can * be used as a mask to align the OA tail pointer. @@ -1353,21 +1369,14 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv, return -EINVAL; } - /* NB: The exponent represents a period as follows: - * - * 80ns * 2^(period_exponent + 1) - * - * Theoretically we can program the OA unit to sample + /* Theoretically we can program the OA unit to sample * every 160ns but don't allow that by default unless * root. - * - * Referring to perf's - * kernel.perf_event_max_sample_rate for a precedent - * (100000 by default); with an OA exponent of 6 we get - * a period of 10.240 microseconds -just under 100000Hz */ - if (value < 6 && !capable(CAP_SYS_ADMIN)) { - DRM_ERROR("Minimum OA sampling exponent is 6 without root privileges\n"); + if (value < i915_oa_min_timer_exponent && + !capable(CAP_SYS_ADMIN)) { + DRM_ERROR("Minimum OA sampling exponent (sysctl dev.i915.oa_min_timer_exponent) is %u without root privileges\n", + i915_oa_min_timer_exponent); return -EACCES; } @@ -1475,6 +1484,15 @@ static struct ctl_table oa_table[] = { .extra1 = &zero, .extra2 = &one, }, + { + .procname = "oa_min_timer_exponent", + .data = &i915_oa_min_timer_exponent, + .maxlen = sizeof(i915_oa_min_timer_exponent), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &oa_exponent_max, + }, {} };