Message-ID: <4B2FA42F.3070408@codemonkey.ws>
Date: Mon, 21 Dec 2009 10:37:03 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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To: Gregory Haskins <gregory.haskins@gmail.com>
CC: Avi Kivity <avi@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       kvm@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       torvalds@linux-foundation.org,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       netdev@vger.kernel.org,
       "alacrityvm-devel@lists.sourceforge.net" 
	<alacrityvm-devel@lists.sourceforge.net>
Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33
References: <4B1D4F29.8020309@gmail.com> <20091218215107.GA14946@elte.hu> <4B2F9582.5000002@gmail.com> <4B2F978D.7010602@redhat.com> <4B2F9C85.7070202@gmail.com>
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On 12/21/2009 10:04 AM, Gregory Haskins wrote:
> No, B and C definitely are, but A is lacking.  And the performance
> suffers as a result in my testing (vhost-net still throws a ton of exits
> as its limited by virtio-pci and only adds about 1Gb/s to virtio-u, far
> behind venet even with things like zero-copy turned off).
>    

How does virtio-pci limit vhost-net?  The only time exits should occur 
are when the guest notifies the host that something has been placed on 
the ring.  Since vhost-net has no tx mitigation scheme right now, the 
result may be that it's taking an io exit on every single packet but 
this is orthogonal to virtio-pci.

Since virtio-pci supports MSI-X, there should be no IO exits on 
host->guest notification other than EOI in the virtual APIC.  This is a 
light weight exit today and will likely disappear entirely with newer 
hardware.

Regards,

Anthony Liguori
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