From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: Network performance with small packets Date: Tue, 1 Feb 2011 23:56:03 +0200 Message-ID: <20110201215603.GA31348@redhat.com> References: <20110127.130240.104065182.davem@davemloft.net> <1296163838.1640.53.camel@localhost.localdomain> <20110128121616.GA8374@redhat.com> <1296523838.30191.39.camel@sridhar.beaverton.ibm.com> <1296594585.26937.817.camel@localhost.localdomain> <20110201212411.GD30770@redhat.com> <1296595955.26937.822.camel@localhost.localdomain> <20110201214211.GB31105@redhat.com> <1296597185.26937.829.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Sridhar Samudrala , Steve Dobbelstein , David Miller , kvm@vger.kernel.org, mashirle@linux.vnet.ibm.com, netdev@vger.kernel.org To: Shirley Ma Return-path: Content-Disposition: inline In-Reply-To: <1296597185.26937.829.camel@localhost.localdomain> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Feb 01, 2011 at 01:53:05PM -0800, Shirley Ma wrote: > On Tue, 2011-02-01 at 23:42 +0200, Michael S. Tsirkin wrote: > > On Tue, Feb 01, 2011 at 01:32:35PM -0800, Shirley Ma wrote: > > > On Tue, 2011-02-01 at 23:24 +0200, Michael S. Tsirkin wrote: > > > > My theory is that the issue is not signalling. > > > > Rather, our queue fills up, then host handles > > > > one packet and sends an interrupt, and we > > > > immediately wake the queue. So the vq > > > > once it gets full, stays full. > > > > > > >From the printk debugging output, it might not be exactly the case. > > The > > > ring gets full, run a bit, then gets full, then run a bit, then > > full... > > > > Yes, but does it get even half empty in between? > > Sometimes, most of them not half of empty in between. But printk slow > down the traffics, so it's not accurate. I think your patch will improve > the performance if it signals guest when half of the ring size is > empty. > > But you manage signal by using TX bytes, There are flags for bytes, buffers and packets. Try playing with any one of them :) Just be sure to use v2. >I would like to change it to > half of the ring size instead for signaling. Is that OK? > > Shirley > > Sure that is why I made it a parameter so you can experiment. -- MST