linux-kernel - Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

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Message-ID: <alpine.DEB.2.00.0912221137380.29381@makko.or.mcafeemobile.com>
Date:	Tue, 22 Dec 2009 11:39:55 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Gregory Haskins <gregory.haskins@...il.com>
cc:	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	kvm@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org,
	"alacrityvm-devel@...ts.sourceforge.net" 
	<alacrityvm-devel@...ts.sourceforge.net>
Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

On Tue, 22 Dec 2009, Gregory Haskins wrote:

> On 12/22/09 1:53 PM, Avi Kivity wrote:
> > I asked why the irqfd/ioeventfd mechanisms are insufficient, and you did not reply.
> > 
> 
> BTW: the ioeventfd issue just fell through the cracks, so sorry about
> that.  Note that I have no specific issue with irqfd ever since the
> lockless IRQ injection code was added.
> 
> ioeventfd turned out to be suboptimal for me in the fast path for two
> reasons:
> 
> 1) the underlying eventfd is called in atomic context.  I had posted
> patches to Davide to address that limitation, but I believe he rejected
> them on the grounds that they are only relevant to KVM.

I thought we addressed this already, in the few hundreds of email we 
exchanged back then :)



> 2) it cannot retain the data field passed in the PIO.  I wanted to have
> one vector that could tell me what value was written, and this cannot be
> expressed in ioeventfd.

Like might have hinted in his reply, couldn't you add data support to the 
ioeventfd bits in KVM, instead of leaking them into mainline eventfd?



- Davide


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