linux-kernel - Re: [PATCH] SCSI: run queue if SCSI device queue isn't ready and queue is idle

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Date:   Wed, 6 Dec 2017 00:45:12 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "axboe@...com" <axboe@...com>, "hare@...e.com" <hare@...e.com>,
        "holger@...lied-asynchrony.com" <holger@...lied-asynchrony.com>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>
Subject: Re: [PATCH] SCSI: run queue if SCSI device queue isn't ready and
 queue is idle

On Tue, Dec 05, 2017 at 04:41:46PM +0000, Bart Van Assche wrote:
> On Wed, 2017-12-06 at 00:28 +0800, Ming Lei wrote:
> > This is still a workaround for RESTART, see my comment before:
> > 
> > 	https://marc.info/?l=linux-block&m=151217500929341&w=2
> 
> A quote from that e-mail: "The theory about using BLK_MQ_S_SCHED_RESTART in
> current way is that we mark it after requests are added to hctx->dispatch".
> Reading that makes me wonder whether you understand the purpose of the
> BLK_MQ_S_SCHED_RESTART flag? That flag is not set after requests are added
> to the dispatch list but after requests have been *removed*. The purpose of
> that flag is to detect whether another thread has run the queue after
> requests were removed from the dispatch list and before these were readded.
> If so, the queue needs to be rerun.

If you want to discuss that, please reply on that thread of '[PATCH 4/7] blk-mq:
Avoid that request processing sta', I will reply on you there too.

-- 
Ming