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From: Ming Lei <ming.lei@redhat.com>
To: "jianchao.wang" <jianchao.w.wang@oracle.com>
Cc: axboe@kernel.dk, bart.vanassche@wdc.com,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] blk-mq: clean up the hctx restart
Date: Tue, 31 Jul 2018 14:16:18 +0800	[thread overview]
Message-ID: <20180731061616.GF15701@ming.t460p> (raw)
In-Reply-To: <8a3383e6-2926-6858-d8f2-671f3cb9e460@oracle.com>

On Tue, Jul 31, 2018 at 01:19:42PM +0800, jianchao.wang wrote:
> Hi Ming
> 
> On 07/31/2018 12:58 PM, Ming Lei wrote:
> > On Tue, Jul 31, 2018 at 12:02:15PM +0800, Jianchao Wang wrote:
> >> Currently, we will always set SCHED_RESTART whenever there are
> >> requests in hctx->dispatch, then when request is completed and
> >> freed the hctx queues will be restarted to avoid IO hang. This
> >> is unnecessary most of time. Especially when there are lots of
> >> LUNs attached to one host, the RR restart loop could be very
> >> expensive.
> > 
> > The big RR restart loop has been killed in the following commit:
> > 
> > commit 97889f9ac24f8d2fc8e703ea7f80c162bab10d4d
> > Author: Ming Lei <ming.lei@redhat.com>
> > Date:   Mon Jun 25 19:31:48 2018 +0800
> > 
> >     blk-mq: remove synchronize_rcu() from blk_mq_del_queue_tag_set()
> > 
> > 
> 
> Oh, sorry, I didn't look into this patch due to its title when iterated the mail list,
> therefore I didn't realize the RR restart loop has already been killed. :)
> 
> The RR restart loop could ensure the fairness of sharing some LLDD resource,
> not just avoid IO hung. Is it OK to kill it totally ?

Yeah, it is, also the fairness might be improved a bit by the way in
commit 97889f9ac24f8d2fc, especially inside driver tag allocation
algorithem.

Thanks,
Ming

  reply	other threads:[~2018-07-31  6:16 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-31  4:02 [RFC] blk-mq: clean up the hctx restart Jianchao Wang
2018-07-31  4:58 ` Ming Lei
2018-07-31  5:19   ` jianchao.wang
2018-07-31  6:16     ` Ming Lei [this message]
2018-08-01  2:17       ` jianchao.wang
2018-08-01  8:58         ` Ming Lei
2018-08-01 13:37           ` jianchao.wang
2018-08-02 10:39             ` Ming Lei
2018-08-02 15:52           ` Bart Van Assche
2018-08-02 15:52             ` Bart Van Assche
2018-08-02 16:58             ` Ming Lei
2018-08-02 17:08               ` Bart Van Assche
2018-08-02 17:08                 ` Bart Van Assche
2018-08-02 17:17                 ` Ming Lei
2018-08-02 17:24                   ` Bart Van Assche
2018-08-02 17:24                     ` Bart Van Assche
2018-08-03  0:35                     ` Ming Lei

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