From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: Network performance with small packets Date: Wed, 2 Feb 2011 20:27:20 +0200 Message-ID: <20110202182720.GB14257@redhat.com> References: <20110202044002.GB3818@redhat.com> <1296626748.26937.852.camel@localhost.localdomain> <1296627549.26937.856.camel@localhost.localdomain> <20110202104832.GA8505@redhat.com> <1296661185.25430.10.camel@localhost.localdomain> <20110202154706.GA12738@redhat.com> <1296666635.25430.35.camel@localhost.localdomain> <20110202173213.GA13907@redhat.com> <1296670311.25430.49.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Krishna Kumar2 , David Miller , kvm@vger.kernel.org, mashirle@linux.vnet.ibm.com, netdev@vger.kernel.org, netdev-owner@vger.kernel.org, Sridhar Samudrala , Steve Dobbelstein To: Shirley Ma Return-path: Received: from mx1.redhat.com ([209.132.183.28]:35379 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754834Ab1BBS1s (ORCPT ); Wed, 2 Feb 2011 13:27:48 -0500 Content-Disposition: inline In-Reply-To: <1296670311.25430.49.camel@localhost.localdomain> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Feb 02, 2011 at 10:11:51AM -0800, Shirley Ma wrote: > On Wed, 2011-02-02 at 19:32 +0200, Michael S. Tsirkin wrote: > > OK, but this should have no effect with a vhost patch > > which should ensure that we don't get an interrupt > > until the queue is at least half empty. > > Right? > > There should be some coordination between guest and vhost. What kind of coordination? With a patched vhost, and a full ring. you should get an interrupt per 100 packets. Is this what you see? And if yes, isn't the guest patch doing nothing then? > We shouldn't > count the TX packets when netif queue is enabled since next guest TX > xmit will free any used buffers in vhost. We need to be careful here in > case we miss the interrupts when netif queue has stopped. > > However we can't change old guest so we can test the patches separately > for guest only, vhost only, and the combination. > > > > > > > > > Yes, it seems unrelated to tx interrupts. > > > > > > The issue is more likely related to latency. > > > > Could be. Why do you think so? > > Since I played with latency hack, I can see performance difference for > different latency. Which hack was that? > > > Do you have anything in > > > mind on how to reduce vhost latency? > > > > > > Thanks > > > Shirley > > > > Hmm, bypassing the bridge might help a bit. > > Are you using tap+bridge or macvtap? > > I am using tap+bridge for TCP_RR test, I think Steven tested macvtap > before. He might have some data from his workload performance > measurement. > > Shirley