linux-kernel - Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle

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Message-ID: <20180119153333.GA14827@ming.t460p>
Date:   Fri, 19 Jan 2018 23:33:33 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "osandov@...com" <osandov@...com>,
        "snitzer@...hat.com" <snitzer@...hat.com>
Subject: Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle

On Fri, Jan 19, 2018 at 03:20:13PM +0000, Bart Van Assche wrote:
> On Fri, 2018-01-19 at 15:26 +0800, Ming Lei wrote:
> > Please see queue_delayed_work_on(), hctx->run_work is shared by all
> > scheduling, once blk_mq_delay_run_hw_queue(100ms) returns, no new
> > scheduling can make progress during the 100ms.
> 
> How about addressing that as follows:
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f7515dd95a36..57f8379a476d 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1403,9 +1403,9 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
>  		put_cpu();
>  	}
>  
> -	kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
> -					 &hctx->run_work,
> -					 msecs_to_jiffies(msecs));
> +	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
> +				    &hctx->run_work,
> +				    msecs_to_jiffies(msecs));
>  }
>  
>  void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
> 
> Bart.

Yes, this one together with Jen's suggestion with returning
BLK_STS_NO_DEV_RESOURCE should fix this issue.

Could you cook a fix for this issue? Otherwise I am happy to do
that.

-- 
Ming