linux-kernel - Re: [PATCH 0/2] eventfd: new EFD

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Message-ID: <4A8D8A28.2050004@redhat.com>
Date:	Thu, 20 Aug 2009 20:38:48 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Davide Libenzi <davidel@...ilserver.org>
CC:	"Michael S. Tsirkin" <mst@...hat.com>, gleb@...hat.com,
	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] eventfd: new EFD_STATE flag

On 08/20/2009 07:20 PM, Davide Libenzi wrote:
>
> I briefly looked at this while in vacation, although I did not reply
> hoping the horrible feeling about this code would go away.
> It didn't.
> I find this to be an ugly and ad-hoc multiplexing of eventfd with added
> functionalities of questionable general use.
> I'm pretty sure you can do better on KVM side, to solve the problem w/out
> littering eventfd.
>
>    

While we could argue about this my feeling is that we should drop this, 
at least until we can quantify what benefit it has and whether there are 
any Davide-acceptable alternatives.

In the meanwhile, we can let vhost-net support edge-triggered interrupts 
only, let qemu terminate those eventfds and convert then to 
level-triggered interrupts (which it can then inject using the existing 
ioctl).  It will keep vhost-net and kvm simpler at the cost of some 
performance penalty to guests using level interrupts.  These suck anyway 
so we'll point users at msi.

-- 
I have a truly marvellous patch that fixes the bug which thisb
signature is too narrow to contain.

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