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

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Date:	Tue, 22 Dec 2009 14:15:38 -0500
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Avi Kivity <avi@...hat.com>
CC:	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 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.

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.

Based on this, it was a better decision to add a ioevent interface to
xinterface.  It neatly solves both problems.

Kind Regards,
-Greg

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