Messages in this thread | | | Date | Fri, 8 Apr 2022 07:24:47 -0700 | Subject | Re: [PATCH -next RFC v2 4/8] blk-mq: don't preempt tag under heavy load | From | Bart Van Assche <> |
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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,
Bart.
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