| Message ID | 20230826112828.58046-1-wahrenst@gmx.net (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | hwrng: bcm2835: Fix hwrng throughput regression | expand |
On Sat, Aug 26, 2023 at 01:28:28PM +0200, Stefan Wahren wrote: > The recent RCU stall fix caused a massive throughput regression of the > hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput > as before the RCU stall fix. > > Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): > > sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 > > cpu_relax ~138025 Bytes / sec > hwrng_msleep(1000) ~13 Bytes / sec > usleep_range(100,200) ~92141 Bytes / sec > > Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") > Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ > Signed-off-by: Stefan Wahren <wahrenst@gmx.net> > --- > drivers/char/hw_random/bcm2835-rng.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c > index e98fcac578d6..3f1b6aaa98ee 100644 > --- a/drivers/char/hw_random/bcm2835-rng.c > +++ b/drivers/char/hw_random/bcm2835-rng.c > @@ -14,6 +14,7 @@ > #include <linux/printk.h> > #include <linux/clk.h> > #include <linux/reset.h> > +#include <linux/delay.h> > > #define RNG_CTRL 0x0 > #define RNG_STATUS 0x4 > @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, > while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { > if (!wait) > return 0; > - hwrng_msleep(rng, 1000); > + usleep_range(100, 200); I think we still need to use the hwrng_msleep function so that the sleep remains cancelable. Maybe just change the 1000 to 100? Jason > } > > num_words = rng_readl(priv, RNG_STATUS) >> 24; > -- > 2.34.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Hi Jason, Am 26.08.23 um 14:34 schrieb Jason A. Donenfeld: > On Sat, Aug 26, 2023 at 01:28:28PM +0200, Stefan Wahren wrote: >> The recent RCU stall fix caused a massive throughput regression of the >> hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput >> as before the RCU stall fix. >> >> Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): >> >> sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 >> >> cpu_relax ~138025 Bytes / sec >> hwrng_msleep(1000) ~13 Bytes / sec >> usleep_range(100,200) ~92141 Bytes / sec >> >> Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") >> Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ >> Signed-off-by: Stefan Wahren <wahrenst@gmx.net> >> --- >> drivers/char/hw_random/bcm2835-rng.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c >> index e98fcac578d6..3f1b6aaa98ee 100644 >> --- a/drivers/char/hw_random/bcm2835-rng.c >> +++ b/drivers/char/hw_random/bcm2835-rng.c >> @@ -14,6 +14,7 @@ >> #include <linux/printk.h> >> #include <linux/clk.h> >> #include <linux/reset.h> >> +#include <linux/delay.h> >> >> #define RNG_CTRL 0x0 >> #define RNG_STATUS 0x4 >> @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, >> while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { >> if (!wait) >> return 0; >> - hwrng_msleep(rng, 1000); >> + usleep_range(100, 200); > > I think we still need to use the hwrng_msleep function so that the sleep > remains cancelable. Maybe just change the 1000 to 100? i found that other hwrng driver like iproc-rng200 (Raspberry Pi 4) also use usleep_range(). Nevertheless here are more numbers: usleep_range(200,400) : 47776 bytes / sec hwrng_msleep(20) : 715 bytes / sec Changing to 100 ms won't be a real gain. > > Jason > >> } >> >> num_words = rng_readl(priv, RNG_STATUS) >> 24; >> -- >> 2.34.1 >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Sat, Aug 26, 2023 at 04:01:58PM +0200, Stefan Wahren wrote: > Hi Jason, > > Am 26.08.23 um 14:34 schrieb Jason A. Donenfeld: > > On Sat, Aug 26, 2023 at 01:28:28PM +0200, Stefan Wahren wrote: > >> The recent RCU stall fix caused a massive throughput regression of the > >> hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput > >> as before the RCU stall fix. > >> > >> Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): > >> > >> sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 > >> > >> cpu_relax ~138025 Bytes / sec > >> hwrng_msleep(1000) ~13 Bytes / sec > >> usleep_range(100,200) ~92141 Bytes / sec > >> > >> Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") > >> Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ > >> Signed-off-by: Stefan Wahren <wahrenst@gmx.net> > >> --- > >> drivers/char/hw_random/bcm2835-rng.c | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c > >> index e98fcac578d6..3f1b6aaa98ee 100644 > >> --- a/drivers/char/hw_random/bcm2835-rng.c > >> +++ b/drivers/char/hw_random/bcm2835-rng.c > >> @@ -14,6 +14,7 @@ > >> #include <linux/printk.h> > >> #include <linux/clk.h> > >> #include <linux/reset.h> > >> +#include <linux/delay.h> > >> > >> #define RNG_CTRL 0x0 > >> #define RNG_STATUS 0x4 > >> @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, > >> while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { > >> if (!wait) > >> return 0; > >> - hwrng_msleep(rng, 1000); > >> + usleep_range(100, 200); > > > > I think we still need to use the hwrng_msleep function so that the sleep > > remains cancelable. Maybe just change the 1000 to 100? > i found that other hwrng driver like iproc-rng200 (Raspberry Pi 4) also > use usleep_range(). > > Nevertheless here are more numbers: > > usleep_range(200,400) : 47776 bytes / sec > hwrng_msleep(20) : 715 bytes / sec > > Changing to 100 ms won't be a real gain. I'm fine with whatever number you want there. Maybe we need a hwrng_usleep_range() that takes into account rng->dying like hwrng_msleep() does? (And iproc-rng200 should probably use that too?) Jason
Hi Jason, Am 26.08.23 um 17:48 schrieb Jason A. Donenfeld: > On Sat, Aug 26, 2023 at 04:01:58PM +0200, Stefan Wahren wrote: >> Hi Jason, >> >> Am 26.08.23 um 14:34 schrieb Jason A. Donenfeld: >>> On Sat, Aug 26, 2023 at 01:28:28PM +0200, Stefan Wahren wrote: >>>> The recent RCU stall fix caused a massive throughput regression of the >>>> hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput >>>> as before the RCU stall fix. >>>> >>>> Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): >>>> >>>> sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 >>>> >>>> cpu_relax ~138025 Bytes / sec >>>> hwrng_msleep(1000) ~13 Bytes / sec >>>> usleep_range(100,200) ~92141 Bytes / sec >>>> >>>> Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") >>>> Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ >>>> Signed-off-by: Stefan Wahren <wahrenst@gmx.net> >>>> --- >>>> drivers/char/hw_random/bcm2835-rng.c | 3 ++- >>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c >>>> index e98fcac578d6..3f1b6aaa98ee 100644 >>>> --- a/drivers/char/hw_random/bcm2835-rng.c >>>> +++ b/drivers/char/hw_random/bcm2835-rng.c >>>> @@ -14,6 +14,7 @@ >>>> #include <linux/printk.h> >>>> #include <linux/clk.h> >>>> #include <linux/reset.h> >>>> +#include <linux/delay.h> >>>> >>>> #define RNG_CTRL 0x0 >>>> #define RNG_STATUS 0x4 >>>> @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, >>>> while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { >>>> if (!wait) >>>> return 0; >>>> - hwrng_msleep(rng, 1000); >>>> + usleep_range(100, 200); >>> I think we still need to use the hwrng_msleep function so that the sleep >>> remains cancelable. Maybe just change the 1000 to 100? >> i found that other hwrng driver like iproc-rng200 (Raspberry Pi 4) also >> use usleep_range(). >> >> Nevertheless here are more numbers: >> >> usleep_range(200,400) : 47776 bytes / sec >> hwrng_msleep(20) : 715 bytes / sec >> >> Changing to 100 ms won't be a real gain. > I'm fine with whatever number you want there. Maybe we need a > hwrng_usleep_range() that takes into account rng->dying like > hwrng_msleep() does? (And iproc-rng200 should probably use that too?) the idea of this patch was to fix the performance regression in upcoming mainline and backport the fix to Linux 6.1 LTS. After that i'm fine with the introduction of hwrng_usleep_range(). Best regards > Jason
On Wed, Aug 30, 2023 at 08:05:39PM +0200, Stefan Wahren wrote: > Hi Jason, > > Am 26.08.23 um 17:48 schrieb Jason A. Donenfeld: > > On Sat, Aug 26, 2023 at 04:01:58PM +0200, Stefan Wahren wrote: > >> Hi Jason, > >> > >> Am 26.08.23 um 14:34 schrieb Jason A. Donenfeld: > >>> On Sat, Aug 26, 2023 at 01:28:28PM +0200, Stefan Wahren wrote: > >>>> The recent RCU stall fix caused a massive throughput regression of the > >>>> hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput > >>>> as before the RCU stall fix. > >>>> > >>>> Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): > >>>> > >>>> sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 > >>>> > >>>> cpu_relax ~138025 Bytes / sec > >>>> hwrng_msleep(1000) ~13 Bytes / sec > >>>> usleep_range(100,200) ~92141 Bytes / sec > >>>> > >>>> Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") > >>>> Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ > >>>> Signed-off-by: Stefan Wahren <wahrenst@gmx.net> > >>>> --- > >>>> drivers/char/hw_random/bcm2835-rng.c | 3 ++- > >>>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c > >>>> index e98fcac578d6..3f1b6aaa98ee 100644 > >>>> --- a/drivers/char/hw_random/bcm2835-rng.c > >>>> +++ b/drivers/char/hw_random/bcm2835-rng.c > >>>> @@ -14,6 +14,7 @@ > >>>> #include <linux/printk.h> > >>>> #include <linux/clk.h> > >>>> #include <linux/reset.h> > >>>> +#include <linux/delay.h> > >>>> > >>>> #define RNG_CTRL 0x0 > >>>> #define RNG_STATUS 0x4 > >>>> @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, > >>>> while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { > >>>> if (!wait) > >>>> return 0; > >>>> - hwrng_msleep(rng, 1000); > >>>> + usleep_range(100, 200); > >>> I think we still need to use the hwrng_msleep function so that the sleep > >>> remains cancelable. Maybe just change the 1000 to 100? > >> i found that other hwrng driver like iproc-rng200 (Raspberry Pi 4) also > >> use usleep_range(). > >> > >> Nevertheless here are more numbers: > >> > >> usleep_range(200,400) : 47776 bytes / sec > >> hwrng_msleep(20) : 715 bytes / sec > >> > >> Changing to 100 ms won't be a real gain. > > I'm fine with whatever number you want there. Maybe we need a > > hwrng_usleep_range() that takes into account rng->dying like > > hwrng_msleep() does? (And iproc-rng200 should probably use that too?) > the idea of this patch was to fix the performance regression in upcoming > mainline and backport the fix to Linux 6.1 LTS. After that i'm fine with > the introduction of hwrng_usleep_range(). No, you've got it backwards, but maybe it's a bit confusing why that is. Originally, lots of drivers called variants of the msleep/usleep functions. But this lead to some subtle bugs when the hwrng subsystem was changing the active RNG or when the driver was unloading or during suspend or a couple of other edge cases. In some cases, I believe there were some interesting deadlocks. The solution to it was to make those sleep calls cancellable with the &rng->dying completion, so those sleeps could break, regardless of the time or the state of timekeeping on the system. The &rng->dying thing was encapsulated in the hwrng_msleep() function, and now it's a rule that any sleeps in hwrng drivers have got to go through that. Now, it sounds like you've come up with a case where hwrng_msleep(1) is too long of a sleep for your purposes. In that case, indeed a usleep variant might be called for. But in doing so, don't _reintroduce the same bug we already fixed_. In other words, don't fix one regression by adding another. Instead, follow the established pattern, and add a hwrng_usleep_whatever() that waits on that same &rng->dying. Jason
diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c index e98fcac578d6..3f1b6aaa98ee 100644 --- a/drivers/char/hw_random/bcm2835-rng.c +++ b/drivers/char/hw_random/bcm2835-rng.c @@ -14,6 +14,7 @@ #include <linux/printk.h> #include <linux/clk.h> #include <linux/reset.h> +#include <linux/delay.h> #define RNG_CTRL 0x0 #define RNG_STATUS 0x4 @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { if (!wait) return 0; - hwrng_msleep(rng, 1000); + usleep_range(100, 200); } num_words = rng_readl(priv, RNG_STATUS) >> 24;
The recent RCU stall fix caused a massive throughput regression of the hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput as before the RCU stall fix. Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 cpu_relax ~138025 Bytes / sec hwrng_msleep(1000) ~13 Bytes / sec usleep_range(100,200) ~92141 Bytes / sec Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ Signed-off-by: Stefan Wahren <wahrenst@gmx.net> --- drivers/char/hw_random/bcm2835-rng.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) -- 2.34.1