linux-kernel - Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

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Message-ID: <alpine.DEB.2.00.1001210857310.8548@makko.or.mcafeemobile.com>
Date:	Thu, 21 Jan 2010 08:58:50 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
cc:	Avi Kivity <avi@...hat.com>, mtosatti@...hat.com,
	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 1/3] eventfd: allow atomic read and waitqueue remove

On Thu, 21 Jan 2010, Michael S. Tsirkin wrote:

> This is a backport of commit: 03db343a6320f780937078433fa7d8da955e6fce
> modified in a way that introduces some code duplication on the one hand,
> but reduces the risk of regressing existing eventfd users on the other
> hand.
> 
> KVM needs a wait to atomically remove themselves from the eventfd
> ->poll() wait queue head, in order to handle correctly their IRQfd
> deassign operation.
> 
> This patch introduces such API, plus a way to read an eventfd from its
> context.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> 
> Avi, Davidel, how about only including the following part for -stable
> then?  Reason is, I still would like to be able to use irqfd there, and
> getting spurious interrupts 100% of times unmask is done isn't a very
> good idea IMO ...

It's the same thing. Unless there are *real* problems in KVM due to the 
spurious ints, I still think this is .33 material.


- Davide


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