From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH] vhost-net: utilize PUBLISH_USED_IDX feature Date: Thu, 20 May 2010 13:48:52 +0930 Message-ID: <201005201348.53702.rusty@rustcorp.com.au> References: <20100518011931.GA21918@redhat.com> <4BF41A33.8090309@redhat.com> <20100519222718.GB4111@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Avi Kivity , davem@davemloft.net, Juan Quintela , "Paul E. McKenney" , Arnd Bergmann , kvm@vger.kernel.org, virtualization@lists.osdl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, alex.williamson@redhat.com, amit.shah@redhat.com To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20100519222718.GB4111@redhat.com> Sender: netdev-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, 20 May 2010 07:57:18 am Michael S. Tsirkin wrote: > On Wed, May 19, 2010 at 08:04:51PM +0300, Avi Kivity wrote: > > On 05/18/2010 04:19 AM, Michael S. Tsirkin wrote: > >> With PUBLISH_USED_IDX, guest tells us which used entries > >> it has consumed. This can be used to reduce the number > >> of interrupts: after we write a used entry, if the guest has not yet > >> consumed the previous entry, or if the guest has already consumed the > >> new entry, we do not need to interrupt. > >> This imporves bandwidth by 30% under some workflows. > >> > >> Signed-off-by: Michael S. Tsirkin > >> --- > >> > >> Rusty, Dave, this patch depends on the patch > >> "virtio: put last seen used index into ring itself" > >> which is currently destined at Rusty's tree. > >> Rusty, if you are taking that one for 2.6.35, please > >> take this one as well. > >> Dave, any objections? > >> > > > > I object: I think the index should have its own cacheline, > > The issue here is that host/guest do not know each > other's cache line size. I guess we could just put it > at offset 128 or something like that ... Rusty? I was assuming you'd put it at the end of the padding. I think it's a silly optimization, but Avi obviously feels strongly about it and I respect his opinion. Please resubmit... Thanks, Rusty.