lkml.org 
[lkml]   [2021]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3] lib/raid6: Reduce high latency by using migrate instead of preempt
Date
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.

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 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(), the latency won't greater than 100us.

This patch beneficial for CONFIG_PREEMPT=y or CONFIG_PREEMPT_RT=y, but no
effect for CONFIG_PREEMPT_VOLUNTARY=y.

Cc: stable@vger.kernel.org
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 # v1
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
\
 
 \ /
  Last update: 2021-12-17 03:17    [W:0.092 / U:0.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site