From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] vhost: Add polling mode Date: Tue, 29 Jul 2014 14:40:18 +0200 Message-ID: <20140729124018.GA14266@redhat.com> References: <20140729080640.GA10185@redhat.com> <20140729104436.GB13388@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: abel.gordon@gmail.com, Alex Glikson , Eran Raichstein , Joel Nider , kvm@vger.kernel.org, kvm-owner@vger.kernel.org, Yossi Kuperman1 To: Razya Ladelsky Return-path: Received: from mx1.redhat.com ([209.132.183.28]:32410 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750907AbaG2MkG (ORCPT ); Tue, 29 Jul 2014 08:40:06 -0400 Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Jul 29, 2014 at 03:23:59PM +0300, Razya Ladelsky wrote: > > > > Hmm there aren't a lot of numbers there :(. Speed increased by 33% but > > by how much? E.g. maybe you are getting from 1Mbyte/sec to 1.3, > > if so it's hard to get excited about it. > > Netperf 1 VM: 1516 MB/sec -> 2046 MB/sec > and for 3 VMs: 4086 MB/sec -> 5545 MB/sec What do you mean by 1 VM? Streaming TCP host to vm? Also, your throughput is somewhat low, it's worth seeing why you can't hit higher speeds. > > Some questions that come to > > mind: what was the message size? I would expect several measurements > > with different values. How did host CPU utilization change? > > > > message size was 64B in order to get the VM to be cpu saturated. > so vhost had 99% cpu and vhost 38%, with the polling patch both had 99%. Hmm so a net loss in throughput/CPU. > > > > What about latency? As we are competing with guest for host CPU, > > would worst-case or average latency suffer? > > > > Polling indeed doesn't make a lot of sense if there aren't enough > available cores. > In these cases polling should not be used. > > Thank you, > Razya OK but scheduler might run vm and vhost on the same cpu even if cores are available. This needs to be detected somehow and polling disabled. > > > > Thanks, > > > > -- > > MST > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > >