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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Daniel Wagner <dwagner@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Mike Galbraith <efault@gmx.de>,
	Christoph Hellwig <hch@infradead.org>,
	Sagi Grimberg <sagi@grimberg.me>, Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq
Date: Tue, 8 Dec 2020 13:57:09 +0100	[thread overview]
Message-ID: <20201208125709.5epgbpmqp56bf243@linutronix.de> (raw)
In-Reply-To: <20201208125224.m2xt66ladp63fa3t@linutronix.de>

On 2020-12-08 13:52:25 [+0100], To Daniel Wagner wrote:
> On 2020-12-08 13:41:48 [+0100], Daniel Wagner wrote:
> > On Tue, Dec 08, 2020 at 12:49:36PM +0100, Sebastian Andrzej Siewior wrote:
> > > On 2020-12-08 12:36:53 [+0100], Daniel Wagner wrote:
> > > > Obvious in this configuration there are no remote completions (verified
> > > > it).
> > > 
> > > do you complete on a remote CPU if you limit the queues to one (this is
> > > untested of course)?
> > 
> > nvme0n1/ completed   11913011 remote    6718563 56.40%
> > 
> > yes, but how is this relevant? I thought Jens complain was about the
> > additional indirection via the softirq context
> > 
> > -		rq->q->mq_ops->complete(rq);
> > +	blk_mq_trigger_softirq(rq);
> > 
> > and not the remote completion path. I can benchmark it out but I don't
> > know if it's really helping in the discussion.
… blurp

Yes, you are right. Even cross-CPU completion for single-queue was
already completing in softirq. So the only change is for multiqueue
devices which you just demonstrated that it does not happen.
Thank you!

Sebastian

  reply	other threads:[~2020-12-08 12:58 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-04 19:13 [PATCH 0/3 v2] blk-mq: Don't complete in IRQ, use llist_head Sebastian Andrzej Siewior
2020-12-04 19:13 ` [PATCH 1/3] blk-mq: Don't complete on a remote CPU in force threaded mode Sebastian Andrzej Siewior
2020-12-08 13:10   ` Christoph Hellwig
2020-12-04 19:13 ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior
2020-12-07 23:52   ` Jens Axboe
2020-12-08  8:22     ` Sebastian Andrzej Siewior
2020-12-08  8:44       ` Daniel Wagner
2020-12-08 11:36         ` Daniel Wagner
2020-12-08 11:49           ` Sebastian Andrzej Siewior
2020-12-08 12:41             ` Daniel Wagner
2020-12-08 12:52               ` Sebastian Andrzej Siewior
2020-12-08 12:57                 ` Sebastian Andrzej Siewior [this message]
2020-12-08 13:27                   ` Daniel Wagner
2020-12-17 16:45         ` Jens Axboe
2020-12-17 16:49           ` Daniel Wagner
2020-12-17 16:54             ` Jens Axboe
2020-12-08 13:13     ` Christoph Hellwig
2020-12-17 16:43       ` Sebastian Andrzej Siewior
2020-12-17 16:55         ` Jens Axboe
2020-12-17 16:58           ` Sebastian Andrzej Siewior
2020-12-17 17:05             ` Daniel Wagner
2020-12-17 18:16           ` Daniel Wagner
2020-12-17 18:22             ` Jens Axboe
2020-12-17 18:41               ` Daniel Wagner
2020-12-17 18:46                 ` Jens Axboe
2020-12-17 19:07                   ` Daniel Wagner
2020-12-17 19:13                     ` Jens Axboe
2020-12-17 19:15                       ` Daniel Wagner
2020-12-04 19:13 ` [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Sebastian Andrzej Siewior
2020-12-08 13:20   ` Christoph Hellwig
2020-12-08 13:28     ` Christoph Hellwig
2020-12-14 20:20     ` Sebastian Andrzej Siewior
  -- strict thread matches above, loose matches on Subject: below --
2021-01-23 20:10 [PATCH v3 0/3] blk-mq: Don't complete in IRQ, use llist_head Sebastian Andrzej Siewior
2021-01-23 20:10 ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior
2021-01-25  7:10   ` Hannes Reinecke
2021-01-25  8:25     ` Christoph Hellwig
2021-01-25  8:30       ` Sebastian Andrzej Siewior
2021-01-25  8:32         ` Christoph Hellwig
2021-01-25  9:29           ` Sebastian Andrzej Siewior
2021-01-25  8:22   ` Christoph Hellwig
2021-01-25  8:49     ` Christoph Hellwig
2021-01-27 11:22   ` Daniel Wagner
2020-10-28  6:56 [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Christoph Hellwig
2020-10-28 14:12 ` [PATCH 1/3] blk-mq: Don't complete on a remote CPU in force threaded mode Sebastian Andrzej Siewior
2020-10-28 14:12   ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior

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