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From: Sagi Grimberg <sagi@grimberg.me>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@lst.de>
Cc: linux-block@vger.kernel.org,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Bart Van Assche <bvanassche@acm.org>
Subject: Re: [RFC PATCH] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING
Date: Wed, 29 Jul 2020 08:42:31 -0700	[thread overview]
Message-ID: <b80fa58d-34f0-cff5-c3f9-7b3d05a8a1ca@grimberg.me> (raw)
In-Reply-To: <20200729102856.GA1563056@T590>


>> In case of BLK_MQ_F_BLOCKING, blk-mq uses SRCU to mark read critical
>> section during dispatching request, then request queue quiesce is based on
>> SRCU. What we want to get is low cost added in fast path.
>>
>> However, from srcu_read_lock/srcu_read_unlock implementation, not see
>> it is quicker than percpu refcount, so use percpu_ref to implement
>> queue quiesce. This usage is cleaner and simpler & enough for implementing
>> queue quiesce. The main requirement is to make sure all read sections to observe
>> QUEUE_FLAG_QUIESCED once blk_mq_quiesce_queue() returns.
>>
>> Also it becomes much easier to add interface of async queue quiesce.
> 
> BTW, no obvious IOPS difference is observed with this patch applied when running
> io on null_blk(blocking, submit_queues=32) in one dual-socket, 32cores system.

Thanks Ming, can you test for non-blocking on the same setup?

I can test some reset storms during traffic.

  reply	other threads:[~2020-07-29 15:42 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28 13:49 [RFC PATCH] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING Ming Lei
2020-07-29 10:28 ` Ming Lei
2020-07-29 15:42   ` Sagi Grimberg [this message]
2020-07-29 15:49     ` Ming Lei
2020-07-29 22:37       ` Sagi Grimberg
2020-07-30 14:53         ` Ming Lei
2020-07-30 16:10           ` Sagi Grimberg
2020-07-30 18:18             ` Keith Busch
2020-07-30 18:23               ` Sagi Grimberg
2020-07-30 19:27                 ` Keith Busch
2020-07-30 19:53                   ` Jens Axboe
2020-07-30 21:03                     ` Sagi Grimberg
2020-07-31  0:33                       ` Ming Lei
2020-07-31  0:24               ` Ming Lei
2020-07-31  0:28             ` Ming Lei
2020-07-29 11:20 ` Johannes Thumshirn
2020-07-29 16:12 ` Keith Busch
2020-07-29 22:16   ` Ming Lei
2020-07-29 22:42     ` Sagi Grimberg
2020-07-30 15:05       ` Ming Lei

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