linux-kernel - RE: [PATCH] block-mq: set both block queue and hardware queue restart bit for restart

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Date:   Thu, 6 Apr 2017 03:38:24 +0000
From:   Long Li <longli@...rosoft.com>
To:     Bart Van Assche <Bart.VanAssche@...disk.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>
CC:     Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>
Subject: RE: [PATCH] block-mq: set both block queue and hardware queue restart
 bit for restart



> -----Original Message-----
> From: Bart Van Assche [mailto:Bart.VanAssche@...disk.com]
> Sent: Wednesday, April 5, 2017 5:32 PM
> To: linux-kernel@...r.kernel.org; linux-block@...r.kernel.org; Long Li
> <longli@...rosoft.com>; axboe@...nel.dk
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>; KY Srinivasan
> <kys@...rosoft.com>; Long Li <longli@...rosoft.com>
> Subject: Re: [PATCH] block-mq: set both block queue and hardware queue
> restart bit for restart
> 
> On Wed, 2017-04-05 at 17:16 -0700, Long Li wrote:
> > Under heavy I/O, one hardware queue may be unable to dispatch any I/O
> > to the device layer. This poses a problem with restarting this
> > hardware queue on I/O finish in blk_mq_sched_restart_queues(), becaue
> > there is nothing pending that will finish in future on this hardware qeueu.
> This will result in deadlock.
> >
> > With this patch, we check for all possible stalled hardware queues
> > when I/O finishes on any hardware queues. This prevents this deadlock.
> >
> > Signed-off-by: Long Li <longli@...rosoft.com>
> > ---
> >  block/blk-mq-sched.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index
> > 09af8ff..f7f3d44 100644
> > --- a/block/blk-mq-sched.c
> > +++ b/block/blk-mq-sched.c
> > @@ -202,7 +202,7 @@ void blk_mq_sched_dispatch_requests(struct
> blk_mq_hw_ctx *hctx)
> >  	 * needing a restart in that case.
> >  	 */
> >  	if (!list_empty(&rq_list)) {
> > -		blk_mq_sched_mark_restart_hctx(hctx);
> > +		blk_mq_sched_mark_restart_queue(hctx);
> >  		did_work = blk_mq_dispatch_rq_list(hctx, &rq_list);
> >  	} else if (!has_sched_dispatch) {
> >  		blk_mq_flush_busy_ctxs(hctx, &rq_list);
> 
> Please drop this patch. I'm working on a better solution.

Thank you. Looking forward to your patch.

> 
> Thanks,
> 
> Bart.