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

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Message-ID: <20090820175540.GA9232@redhat.com>
Date:	Thu, 20 Aug 2009 20:55:41 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>, 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 Thu, Aug 20, 2009 at 08:38:48PM +0300, Avi Kivity wrote:
> 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 thought the point was to move assigned devices out of KVM?

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