* [PATCH v2] lib/raid6: Reduce high latency by using migrate instead of preempt
@ 2021-12-16 9:26 Yajun Deng
2021-12-16 19:23 ` Song Liu
0 siblings, 1 reply; 3+ messages in thread
From: Yajun Deng @ 2021-12-16 9:26 UTC (permalink / raw)
To: song, pmenzel, williams, masahiroy
Cc: linux-kernel, linux-rt-users, linux-raid, Yajun Deng
We found an abnormally high latency when executing modprobe raid6_pq, the
latency is greater than 1.2s when CONFIG_PREEMPT_VOLUNTARY=y, greater than
67ms when CONFIG_PREEMPT=y, and greater than 16ms when CONFIG_PREEMPT_RT=y.
This is caused by ksoftirqd fail to scheduled due to disable preemption,
this time is too long and unreasonable.
Reduce high latency by using migrate_disabl()/emigrate_enable() instead of
preempt_disable()/preempt_enable().
How to reproduce:
- Install cyclictest
sudo apt install rt-tests
- Run cyclictest example in one terminal
sudo cyclictest -S -p 95 -d 0 -i 1000 -D 24h -m
- Modprobe raid6_pq in another terminal
sudo modprobe raid6_pq
This patch beneficial for CONFIG_PREEMPT=y and CONFIG_PREEMPT_RT=y, but
no effect for CONFIG_PREEMPT_VOLUNTARY=y.
Fixes: fe5cbc6e06c7 ("md/raid6 algorithms: delta syndrome functions")
Fixes: cc4589ebfae6 ("Rename raid6 files now they're in a 'raid6' directory.")
Link: https://lore.kernel.org/linux-raid/b06c5e3ef3413f12a2c2b2a241005af9@linux.dev/T/#t
Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
lib/raid6/algos.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
index 6d5e5000fdd7..21611d05c34c 100644
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -162,7 +162,7 @@ static inline const struct raid6_calls *raid6_choose_gen(
perf = 0;
- preempt_disable();
+ migrate_disable();
j0 = jiffies;
while ((j1 = jiffies) == j0)
cpu_relax();
@@ -171,7 +171,7 @@ static inline const struct raid6_calls *raid6_choose_gen(
(*algo)->gen_syndrome(disks, PAGE_SIZE, *dptrs);
perf++;
}
- preempt_enable();
+ migrate_enable();
if (perf > bestgenperf) {
bestgenperf = perf;
@@ -186,7 +186,7 @@ static inline const struct raid6_calls *raid6_choose_gen(
perf = 0;
- preempt_disable();
+ migrate_disable();
j0 = jiffies;
while ((j1 = jiffies) == j0)
cpu_relax();
@@ -196,7 +196,7 @@ static inline const struct raid6_calls *raid6_choose_gen(
PAGE_SIZE, *dptrs);
perf++;
}
- preempt_enable();
+ migrate_enable();
if (best == *algo)
bestxorperf = perf;
--
2.32.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] lib/raid6: Reduce high latency by using migrate instead of preempt
2021-12-16 9:26 [PATCH v2] lib/raid6: Reduce high latency by using migrate instead of preempt Yajun Deng
@ 2021-12-16 19:23 ` Song Liu
2021-12-17 21:55 ` Daniel Vacek
0 siblings, 1 reply; 3+ messages in thread
From: Song Liu @ 2021-12-16 19:23 UTC (permalink / raw)
To: Yajun Deng
Cc: Paul Menzel, williams, masahiroy, open list, linux-rt-users, linux-raid
On Thu, Dec 16, 2021 at 1:27 AM Yajun Deng <yajun.deng@linux.dev> wrote:
>
> We found an abnormally high latency when executing modprobe raid6_pq, the
> latency is greater than 1.2s when CONFIG_PREEMPT_VOLUNTARY=y, greater than
> 67ms when CONFIG_PREEMPT=y, and greater than 16ms when CONFIG_PREEMPT_RT=y.
>
> This is caused by ksoftirqd fail to scheduled due to disable preemption,
> this time is too long and unreasonable.
>
> Reduce high latency by using migrate_disabl()/emigrate_enable() instead of
> preempt_disable()/preempt_enable().
>
> How to reproduce:
> - Install cyclictest
> sudo apt install rt-tests
> - Run cyclictest example in one terminal
> sudo cyclictest -S -p 95 -d 0 -i 1000 -D 24h -m
> - Modprobe raid6_pq in another terminal
> sudo modprobe raid6_pq
>
> This patch beneficial for CONFIG_PREEMPT=y and CONFIG_PREEMPT_RT=y, but
> no effect for CONFIG_PREEMPT_VOLUNTARY=y.
>
> Fixes: fe5cbc6e06c7 ("md/raid6 algorithms: delta syndrome functions")
> Fixes: cc4589ebfae6 ("Rename raid6 files now they're in a 'raid6' directory.")
> Link: https://lore.kernel.org/linux-raid/b06c5e3ef3413f12a2c2b2a241005af9@linux.dev/T/#t
> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
Updated the patch and CC'ed stable. It should make to LTS kernels.
Thanks,
Song
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] lib/raid6: Reduce high latency by using migrate instead of preempt
2021-12-16 19:23 ` Song Liu
@ 2021-12-17 21:55 ` Daniel Vacek
0 siblings, 0 replies; 3+ messages in thread
From: Daniel Vacek @ 2021-12-17 21:55 UTC (permalink / raw)
To: Song Liu
Cc: Yajun Deng, Paul Menzel, williams, masahiroy, open list,
linux-rt-users, linux-raid
NACK. This is a BUG.
--nX
On Fri, Dec 17, 2021 at 1:02 AM Song Liu <song@kernel.org> wrote:
>
> On Thu, Dec 16, 2021 at 1:27 AM Yajun Deng <yajun.deng@linux.dev> wrote:
> >
> > We found an abnormally high latency when executing modprobe raid6_pq, the
> > latency is greater than 1.2s when CONFIG_PREEMPT_VOLUNTARY=y, greater than
> > 67ms when CONFIG_PREEMPT=y, and greater than 16ms when CONFIG_PREEMPT_RT=y.
> >
> > This is caused by ksoftirqd fail to scheduled due to disable preemption,
> > this time is too long and unreasonable.
> >
> > Reduce high latency by using migrate_disabl()/emigrate_enable() instead of
> > preempt_disable()/preempt_enable().
> >
> > How to reproduce:
> > - Install cyclictest
> > sudo apt install rt-tests
> > - Run cyclictest example in one terminal
> > sudo cyclictest -S -p 95 -d 0 -i 1000 -D 24h -m
> > - Modprobe raid6_pq in another terminal
> > sudo modprobe raid6_pq
> >
> > This patch beneficial for CONFIG_PREEMPT=y and CONFIG_PREEMPT_RT=y, but
> > no effect for CONFIG_PREEMPT_VOLUNTARY=y.
> >
> > Fixes: fe5cbc6e06c7 ("md/raid6 algorithms: delta syndrome functions")
> > Fixes: cc4589ebfae6 ("Rename raid6 files now they're in a 'raid6' directory.")
> > Link: https://lore.kernel.org/linux-raid/b06c5e3ef3413f12a2c2b2a241005af9@linux.dev/T/#t
> > Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
>
> Updated the patch and CC'ed stable. It should make to LTS kernels.
>
> Thanks,
> Song
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-12-17 21:55 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-12-16 9:26 [PATCH v2] lib/raid6: Reduce high latency by using migrate instead of preempt Yajun Deng
2021-12-16 19:23 ` Song Liu
2021-12-17 21:55 ` Daniel Vacek
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