Re: [PATCH] RFC: mmc: block: replace semaphore with freezing - Russell King

From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Binoy Jayan <binoy.jayan@linaro.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Chunyan Zhang <zhang.chunyan@linaro.org>,
	Baolin Wang <baolin.wang@linaro.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Jiri Kosina <jikos@kernel.org>
Subject: Re: [PATCH] RFC: mmc: block: replace semaphore with freezing
Date: Tue, 22 Nov 2016 09:10:23 +0000	[thread overview]
Message-ID: <20161122091023.GS1041@n2100.armlinux.org.uk> (raw)
In-Reply-To: <CACRpkdagS-7kaYCd2Sq0vLR8+19Mmckx=CuCqPv+HheRk8Cm7w@mail.gmail.com>

On Tue, Nov 22, 2016 at 09:54:18AM +0100, Linus Walleij wrote:
> On Wed, Nov 16, 2016 at 5:32 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wednesday, November 16, 2016 4:20:47 PM CET Linus Walleij wrote:
> >> On Wed, Nov 16, 2016 at 1:46 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> >>
> >> > Well, we had a session at the KS regarding usage of the freezer on
> >> > kernel threads and the conclusion was to get rid of that (as opposed
> >> > to freezing user space, which is necessary IMO).  So this change would
> >> > go in the opposite direction.
> >>
> >> Aha so I should not make this thread look like everyone else, instead
> >> everyone else should look like this thread, haha
> >>
> >> Ah well, I'll just drop it.
> >
> > It would still be good to remove the semaphore and do something else,
> > as we also want to remove all semaphores. ;-)
> >
> > We could check "mq->flags & MMC_QUEUE_SUSPENDED" in the kthread to see
> > if the queue is currently suspended, and otherwise go to sleep there,
> > and then call wake_up() in the resume function.
> 
> Hm... so simply:
> 
> if (mq->flags & MMC_QUEUE_SUSPENDED)
>   schedule();
> 
> ?

No, the schedule() is required when there are no more requests to
process, so the thread doesn't spin waiting for the next request to
appear.

-- 
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