[PATCH] lib/raid6: fix abnormally high latency

Yajun Deng
2021-12-14T03:00:41Z

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 disable the preemption, this time is too long and
unreasonable. We just need to disable migration. so used migrate_disable()/
migrate_enable() instead of preempt_disable()/preempt_enable(). This is
beneficial for CONFIG_PREEMPT=y or CONFIG_PREEMPT_RT=y, but no effect for
CONFIG_PREEMPT_VOLUNTARY=y.

Fixes: fe5cbc6e06c7 ("md/raid6 algorithms: delta syndrome functions")
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