linux-kernel - Re: [PATCH] hrtimer: make epoll_wait() use the hrtimer range feature

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Message-ID: <alpine.LFD.2.00.1008270059240.2768@localhost.localdomain>
Date:	Fri, 27 Aug 2010 01:02:09 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Davide Libenzi <davidel@...ilserver.org>
cc:	Shawn Bohrer <shawn.bohrer@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] hrtimer: make epoll_wait() use the hrtimer range
 feature

On Thu, 26 Aug 2010, Davide Libenzi wrote:
> On Sun, 8 Aug 2010, Shawn Bohrer wrote:
> 
> > This make epoll use hrtimers for the timeout value which prevents
> > epoll_wait() from timing out up to a millisecond early.
> > 
> > This mirrors the behavior of select() and poll().
> 
> I saw this now, since I got notifications from Andrew's patch machine.
> Is this really needed?

Yes, as it is the last user space interface which is jiffies based.

> Is that really worth the extra code in the fast path?

It's not that much overhead and we had no complaints when we converted
everything else

> Aren't we breaking existing behavior?

We had no problems when we moved all the other interfaces over

> I have some doubts.

/me not - though I need to look at the patch itself

Thanks,

	tglx


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