From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33 Date: Mon, 21 Dec 2009 10:37:03 -0600 Message-ID: <4B2FA42F.3070408@codemonkey.ws> References: <4B1D4F29.8020309@gmail.com> <20091218215107.GA14946@elte.hu> <4B2F9582.5000002@gmail.com> <4B2F978D.7010602@redhat.com> <4B2F9C85.7070202@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Ingo Molnar , kvm@vger.kernel.org, Andrew Morton , torvalds@linux-foundation.org, "linux-kernel@vger.kernel.org" , netdev@vger.kernel.org, "alacrityvm-devel@lists.sourceforge.net" To: Gregory Haskins Return-path: Received: from mail-yw0-f182.google.com ([209.85.211.182]:44496 "EHLO mail-yw0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750891AbZLUQhN (ORCPT ); Mon, 21 Dec 2009 11:37:13 -0500 In-Reply-To: <4B2F9C85.7070202@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: 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