Messages in this thread | | | Subject | Re: [PATCH -next RFC v2 4/8] blk-mq: don't preempt tag under heavy load | From | "yukuai (C)" <> | Date | Sat, 9 Apr 2022 10:38:14 +0800 |
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在 2022/04/08 22:24, Bart Van Assche 写道: > On 4/8/22 00:39, Yu Kuai wrote: >> The idle way to disable tag preemption is to track how many tags are > > idle -> ideal? > >> available, and wait directly in blk_mq_get_tag() if free tags are >> very little. However, this is out of reality because fast path is >> affected. >> >> As 'ws_active' is only updated in slow path, this patch disable tag >> preemption if 'ws_active' is greater than 8, which means there are many >> threads waiting for tags already. >> >> Once tag preemption is disabled, there is a situation that can cause >> performance degration(or io hung in extreme scenarios): the waitqueue > > degration -> degradation? > >> diff --git a/block/blk-mq.h b/block/blk-mq.h >> index 2615bd58bad3..b49b20e11350 100644 >> --- a/block/blk-mq.h >> +++ b/block/blk-mq.h >> @@ -156,6 +156,7 @@ struct blk_mq_alloc_data { >> /* allocate multiple requests/tags in one go */ >> unsigned int nr_tags; >> + bool preemption; >> struct request **cached_rq; > > Please change "preemption" into "preempt".
Thanks for your advice, will change that and previous spelling mistakes.
Kuai > > Thanks, > > Bart. > > . >
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