lib/raid6: fix abnormally high latency

PATCH New Yajun Deng 1 participant 1 message Dec 14, 2021

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Yajun Deng

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2021-12-14 03:00 UTC #0 lore raw

PATCH 1/1 lib/raid6: fix abnormally high latency

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 <[email protected]>

---
 lib/raid6/algos.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

lib/raid6/algos.c +4 -4

index 6d5e5000fdd7..21611d05c34c 100644
@@ -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;

Signature · 1 line

2.32.0