From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] vhost-net: utilize PUBLISH_USED_IDX feature Date: Wed, 19 May 2010 20:04:51 +0300 Message-ID: <4BF41A33.8090309@redhat.com> References: <20100518011931.GA21918@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, Juan Quintela , Rusty Russell , "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: <20100518011931.GA21918@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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, and that it should be documented before merging. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.