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

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Date:   Fri, 19 Jan 2018 16:06:01 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "ming.lei@...hat.com" <ming.lei@...hat.com>
CC:     "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>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "snitzer@...hat.com" <snitzer@...hat.com>
Subject: Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle

On Fri, 2018-01-19 at 23:33 +0800, Ming Lei wrote:
> 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.

Hello Ming,

I will look further into this.

Bart.