From: Christoph Hellwig <hch@lst.de>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Liu Xiang <liu.xiang@zlingsmart.com>,
"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
liuxiang_1999@126.com, Christoph Hellwig <hch@lst.de>,
Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH] mmc: block: use REQ_HIPRI flag to complete request directly in own complete workqueue
Date: Fri, 5 Feb 2021 17:22:21 +0100 [thread overview]
Message-ID: <20210205162221.GA27114@lst.de> (raw)
In-Reply-To: <CAPDyKFpOFRGdd0L4Sx9ynV3O_9YJvO=2VBxvWYTfBHjabiDaUg@mail.gmail.com>
On Fri, Feb 05, 2021 at 03:24:06PM +0100, Ulf Hansson wrote:
> On Thu, 21 Jan 2021 at 09:13, Liu Xiang <liu.xiang@zlingsmart.com> wrote:
> >
> > After commit "40d09b53bfc557af7481b9d80f060a7ac9c7d314", request is
> > completed in softirq. This may cause the system to suffer bad preemptoff
> > time.
> > The mmc driver has its own complete workqueue, but it can not work
> > well now.
> > The REQ_HIPRI flag can be used to complete request directly in its own
> > complete workqueue and the preemptoff problem could be avoided.
>
> I am trying to understand all of the problem, but I don't quite get
> it, sorry. Would it be possible for you to extend the description in
> the commit message a bit?
Yes, the message sounds weird. The mentioned commit should obviously
not make any difference for drivers not using it.
> More exactly, what will happen if we tag a request with REQ_HIPRI
> before completing it? Apologize for my ignorance, but I am currently a
> bit overwhelmed with work, so I didn't have the time to really look it
> up myself.
Drivers must never set REQ_HIPRI! This is a flag that is set by
the submitter, and actually cleared for most drivers that don't support
it by the block layer.
next prev parent reply other threads:[~2021-02-05 22:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 8:13 [PATCH] mmc: block: use REQ_HIPRI flag to complete request directly in own complete workqueue Liu Xiang
2021-02-05 14:24 ` Ulf Hansson
2021-02-05 16:22 ` Christoph Hellwig [this message]
2021-03-23 15:40 xiang fei
2021-03-23 19:11 ` Christoph Hellwig
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