From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] virtio-ring: Use threshold for switching to indirect descriptors Date: Sun, 04 Dec 2011 17:16:59 +0200 Message-ID: <4EDB8EEB.4070309@redhat.com> References: <1322669511.3985.8.camel@lappy> <87wrahrp0u.fsf@rustcorp.com.au> <20111201075847.GA5479@redhat.com> <1322726977.3259.3.camel@lappy> <20111201102640.GB8822@redhat.com> <87zkfbre9x.fsf@rustcorp.com.au> <1322913028.3782.4.camel@lappy> <4EDB5EF0.2010909@redhat.com> <20111204120132.GB18758@redhat.com> <4EDB624A.3030403@redhat.com> <20111204151148.GA21851@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20111204151148.GA21851@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: markmc@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Sasha Levin List-Id: virtualization@lists.linuxfoundation.org On 12/04/2011 05:11 PM, Michael S. Tsirkin wrote: > > There's also the used ring, but that's a > > mistake if you have out of order completion. We should have used copying. > > Seems unrelated... unless you want used to be written into > descriptor ring itself? The avail/used rings are in addition to the regular ring, no? If you copy descriptors, then it goes away. > But, I don't really know why does virtio ring insist on > making the 3 buffers (avail/used/descriptor) > physically contigious. Rusty? Let's drop them instead. > > > 16kB worth of descriptors is 1024 entries. With 4kB buffers, that's 4MB > > worth of data, or 4 ms at 10GbE line speed. With 1500 byte buffers it's > > just 1.5 ms. In any case I think it's sufficient. > > Right. So I think that without indirect, we waste about 3 entries > per packet for virtio header and transport etc headers. That does suck. Are there issues in increasing the ring size? Or making it discontiguous? Can you take a peek at how Xen manages its rings? They have the same problems we do. -- error compiling committee.c: too many arguments to function