linux-kernel - Re: [PATCH] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready

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Message-Id: <201205011551.33699.rjw@sisk.pl>
Date:	Tue, 1 May 2012 15:51:33 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	NeilBrown <neilb@...e.de>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>, markgross@...gnar.org,
	Matthew Garrett <mjg@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	Brian Swetland <swetland@...gle.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready

On Tuesday, May 01, 2012, NeilBrown wrote:
> On Mon, 30 Apr 2012 22:33:48 -0700 Arve Hjønnevåg <arve@...roid.com> wrote:
> 
> > When an epoll_event, that has the EPOLLWAKEUP flag set, is ready, a
> > wakeup_source will be active to prevent suspend. This can be used to
> > handle wakeup events from a driver that support poll, e.g. input, if
> > that driver wakes up the waitqueue passed to epoll before allowing
> > suspend.
> > 
> > Signed-off-by: Arve Hjønnevåg <arve@...roid.com>
> > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> 
> Thanks.
>  Reviewed-by: NeilBrown <neilb@...e.de>

Thanks a lot for your involvement here!

> However:
> 1/ I think all references to "automatic system suspend" can be replaced with
>    "system suspend" as an active wakeup_source disables any suspend, no matter
>    it's source

OK, I'll change that when applying the patch (although that only applies to
suspends taking the wakeup events signaling through wakeup sources into
account).

> 2/ I reserve to right to submit for discussion a later patch which removes
>    the ep->ws in favour or some other exclusion mechanism :-)

Well, you can alwyas do that. :-)  Of course, when the patch goes to Linus,
we'll have to be careful about changes visible to user space, though.

Thanks,
Rafael
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