linux-kernel - Re: [RFC] blk-mq: clean up the hctx restart

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Date:   Tue, 31 Jul 2018 12:58:06 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     axboe@...nel.dk, bart.vanassche@....com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] blk-mq: clean up the hctx restart

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@...hat.com>
Date:   Mon Jun 25 19:31:48 2018 +0800

    blk-mq: remove synchronize_rcu() from blk_mq_del_queue_tag_set()


Thanks,
Ming