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From: "tj@kernel.org" <tj@kernel.org>
To: Bart Van Assche <Bart.VanAssche@wdc.com>
Cc: "axboe@kernel.dk" <axboe@kernel.dk>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"kernel-team@fb.com" <kernel-team@fb.com>,
	"oleg@redhat.com" <oleg@redhat.com>, "hch@lst.de" <hch@lst.de>,
	"jianchao.w.wang@oracle.com" <jianchao.w.wang@oracle.com>,
	"osandov@fb.com" <osandov@fb.com>
Subject: Re: [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme
Date: Tue, 12 Dec 2017 13:44:32 -0800	[thread overview]
Message-ID: <20171212214432.GL3919388@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <1513114630.2999.48.camel@wdc.com>

Hello, Bart.

On Tue, Dec 12, 2017 at 09:37:11PM +0000, Bart Van Assche wrote:
> Have you considered the following instead of introducing MQ_RQ_IDLE and
> MQ_RQ_IN_FLIGHT? I think this could help to limit the number of new atomic
> operations introduced in the hot path by this patch series.

But nothing in the hot paths is atomic.

> static inline bool blk_mq_rq_in_flight(struct request *rq)
> {
> 	return list_empty(&rq->queuelist);
> }

And the fact that we encode the generation number and state into a
single variable contributes to not needing atomic operations.
Breaking up the state and generation like the above would need more
synchronization, not less.

Thanks.

-- 
tejun

  reply	other threads:[~2017-12-12 21:44 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-12 19:01 [PATCHSET v2] blk-mq: reimplement timeout handling Tejun Heo
2017-12-12 19:01 ` [PATCH 1/6] blk-mq: protect completion path with RCU Tejun Heo
2017-12-13  3:30   ` jianchao.wang
2017-12-13 16:13     ` Tejun Heo
2017-12-14  2:09       ` jianchao.wang
2017-12-14 17:01   ` Bart Van Assche
2017-12-14 18:14     ` tj
2017-12-12 19:01 ` [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme Tejun Heo
2017-12-12 21:37   ` Bart Van Assche
2017-12-12 21:44     ` tj [this message]
2017-12-13  5:07   ` jianchao.wang
2017-12-13 16:13     ` Tejun Heo
2017-12-14 18:51   ` Bart Van Assche
2017-12-14 19:19     ` tj
2017-12-14 21:13       ` Bart Van Assche
2017-12-15 13:30         ` tj
2017-12-14 20:20     ` Peter Zijlstra
2017-12-14 21:42       ` Bart Van Assche
2017-12-14 21:54         ` Peter Zijlstra
2017-12-15  2:12           ` jianchao.wang
2017-12-15  7:31             ` Peter Zijlstra
2017-12-15 15:14               ` jianchao.wang
2017-12-15  2:39           ` Mike Galbraith
2017-12-15 13:50       ` tj
2017-12-12 19:01 ` [PATCH 3/6] blk-mq: use blk_mq_rq_state() instead of testing REQ_ATOM_COMPLETE Tejun Heo
2017-12-12 19:01 ` [PATCH 4/6] blk-mq: make blk_abort_request() trigger timeout path Tejun Heo
2017-12-14 18:56   ` Bart Van Assche
2017-12-14 19:26     ` tj
2017-12-12 19:01 ` [PATCH 5/6] blk-mq: remove REQ_ATOM_COMPLETE usages from blk-mq Tejun Heo
2017-12-12 19:01 ` [PATCH 6/6] blk-mq: remove REQ_ATOM_STARTED Tejun Heo
2017-12-12 22:20   ` Bart Van Assche
2017-12-12 22:22     ` tj
2017-12-12 20:23 ` [PATCHSET v2] blk-mq: reimplement timeout handling Jens Axboe
2017-12-12 21:40   ` Tejun Heo
2017-12-20 23:41 ` Bart Van Assche
2017-12-21  0:08   ` tj
2017-12-21  1:00     ` Bart Van Assche
  -- strict thread matches above, loose matches on Subject: below --
2017-12-09 19:25 [PATCHSET] " Tejun Heo
2017-12-09 19:25 ` [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme Tejun Heo
2017-12-12 10:09   ` Peter Zijlstra
2017-12-12 18:02     ` Tejun Heo
2017-12-12 10:10   ` Peter Zijlstra
2017-12-12 18:03     ` Tejun Heo
2017-12-12 11:56   ` Peter Zijlstra
2017-12-12 18:04     ` Tejun Heo

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