From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC PATCH 1/1] vhost: TX used buffer guest signal accumulation Date: Fri, 29 Oct 2010 10:03:47 +0200 Message-ID: <20101029080347.GA22688@redhat.com> References: <1288216693.17571.38.camel@localhost.localdomain> <1288240804.14342.1.camel@localhost.localdomain> <20101028052021.GD5599@redhat.com> <1288294355.11251.20.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Shirley Ma Return-path: Content-Disposition: inline In-Reply-To: <1288294355.11251.20.camel@localhost.localdomain> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, Oct 28, 2010 at 12:32:35PM -0700, Shirley Ma wrote: > On Thu, 2010-10-28 at 07:20 +0200, Michael S. Tsirkin wrote: > > My concern is this can delay signalling for unlimited time. > > Could you pls test this with guests that do not have > > 2b5bbe3b8bee8b38bdc27dd9c0270829b6eb7eeb > > b0c39dbdc204006ef3558a66716ff09797619778 > > that is 2.6.31 and older? > > The patch only induces delay signaling unlimited time when there is no > TX packet to transmit. I thought TX signaling only noticing guest to > release the used buffers, anything else beside this? Right, that's it I think. For newer kernels we orphan the skb on xmit so we don't care that much about completing them. This does rely on an undocumented assumption about guest behaviour though. > I tested rhel5u5 guest (2.6.18 kernel), it works fine. I checked the two > commits log, I don't think this patch could cause any issue w/o these > two patches. > > Also I found a big TX regression for old guest and new guest. For old > guest, I am able to get almost 11Gb/s for 2K message size, but for the > new guest kernel, I can only get 3.5 Gb/s with the patch and same host. > I will dig it why. > > thanks > Shirley