Re: [PATCH] bcache: add cond_resched() in __bch_cache_cmp()

From: Shile Zhang
Date: Thu Mar 07 2019 - 10:07:21 EST

On 2019/3/7 18:34, Coly Li wrote:
On 2019/3/7 1:15 äå, shile.zhang@xxxxxxxxxxxxxxxxx wrote:
From: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>

Read /sys/fs/bcache/<uuid>/cacheN/priority_stats can take very long
time with huge cache after long run.

Signed-off-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
Hi Shile,

Do you test your change ? It will be helpful with more performance data
(what problem that you improved).

In case of 960GB SSD cache device, once read of the 'priority_stats' costs about 600ms in our test environment.

The perf tool shown that near 50% CPU time consumed by 'sort()', this means once sort will hold the CPU near 300ms.

In our case, the statistics collector reads the 'priority_stats' periodically, it will trigger the schedule latency jitters of the

task which shared same CPU core.


Coly Li

drivers/md/bcache/sysfs.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 557a8a3..028fea1 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -897,6 +897,7 @@ static void bch_cache_set_internal_release(struct kobject *k)
static int __bch_cache_cmp(const void *l, const void *r)
+ cond_resched();
return *((uint16_t *)r) - *((uint16_t *)l);