From: Sagi Grimberg <sagi@grimberg.me>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
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 15:37:27 -0700 [thread overview]
Message-ID: <f3ead535-070d-40ec-08b8-56e2c1cd7ba4@grimberg.me> (raw)
In-Reply-To: <20200729154957.GD1698748@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?
>
> OK, I can do that, but this patch supposes to not affect non-blocking,
> care to share your motivation for testing non-blocking?
I think it will be a significant improvement to have a single code path.
The code will be more robust and we won't need to face issues that are
specific for blocking.
If the cost is negligible, I think the upside is worth it.
next prev parent reply other threads:[~2020-07-29 22:37 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
2020-07-29 15:49 ` Ming Lei
2020-07-29 22:37 ` Sagi Grimberg [this message]
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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