From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753995AbdJIKkn (ORCPT <rfc822;w@1wt.eu>);
        Mon, 9 Oct 2017 06:40:43 -0400
Received: from mx1.redhat.com ([209.132.183.28]:45992 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751550AbdJIKkl (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 9 Oct 2017 06:40:41 -0400
DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 842FD8553E
Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com
Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=ming.lei@redhat.com
Date: Mon, 9 Oct 2017 18:40:20 +0800
From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@fb.com>, linux-block@vger.kernel.org,
        Mike Snitzer <snitzer@redhat.com>, dm-devel@redhat.com,
        Bart Van Assche <bart.vanassche@sandisk.com>,
        Laurence Oberman <loberman@redhat.com>,
        Paolo Valente <paolo.valente@linaro.org>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Tom Nguyen <tom81094@gmail.com>, linux-kernel@vger.kernel.org,
        linux-scsi@vger.kernel.org, Omar Sandoval <osandov@fb.com>
Subject: Re: [PATCH V5 7/7] blk-mq-sched: don't dequeue request until all in
 ->dispatch are flushed
Message-ID: <20171009104019.GC22168@ming.t460p>
References: <20170930102720.30219-1-ming.lei@redhat.com>
 <20170930102720.30219-8-ming.lei@redhat.com>
 <20171003091128.GD21184@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171003091128.GD21184@infradead.org>
User-Agent: Mutt/1.8.3 (2017-05-23)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Mon, 09 Oct 2017 10:40:41 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Oct 03, 2017 at 02:11:28AM -0700, Christoph Hellwig wrote:
> This looks good in general:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> 
> Minor nitpicks below:
> 
> >  	const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
> 
> This is now only tested once, so you can remove the local variable
> for it.

There are still two users of the local variable, so I suggest to
keep it.

> 
> > +		/*
> > +		 * We may clear DISPATCH_BUSY just after it
> > +		 * is set from another context, the only cost
> > +		 * is that one request is dequeued a bit early,
> > +		 * we can survive that. Given the window is
> > +		 * small enough, no need to worry about performance
> > +		 * effect.
> > +		 */
> 
> Use your 80 line real estate for comments please.

OK.

> 
> >  	if (!has_sched_dispatch)
> > +		if (!q->queue_depth) {
> > +			blk_mq_flush_busy_ctxs(hctx, &rq_list);
> > +			blk_mq_dispatch_rq_list(q, &rq_list);
> > +		} else {
> > +			blk_mq_do_dispatch_ctx(q, hctx);
> > +		}
> > +	} else {
> >  		blk_mq_do_dispatch_sched(q, e, hctx);
> > +	}
> 
> Maybe flatten this out to:
> 
> 	if (e && e->type->ops.mq.dispatch_request) {
> 		blk_mq_do_dispatch_sched(q, e, hctx);
> 	} else if (q->queue_depth) {
> 		blk_mq_do_dispatch_ctx(q, hctx);
> 	} else {
> 		blk_mq_flush_busy_ctxs(hctx, &rq_list);
> 		blk_mq_dispatch_rq_list(q, &rq_list);
> 	}
> 

OK.


-- 
Ming