From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-2535-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [66.179.20.138]) by lists.oasis-open.org (Postfix) with ESMTP id D5CA958191A0 for ; Tue, 12 Sep 2017 09:24:37 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <0f0e1b94-2a46-689c-dbb3-0d578cc8df33@redhat.com> References: <20160915223915.qjlnlvf2w7u37bu3@redhat.com> <0f0e1b94-2a46-689c-dbb3-0d578cc8df33@redhat.com> From: Willem de Bruijn Date: Tue, 12 Sep 2017 12:23:56 -0400 Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [virtio-dev] Re: packed ring layout proposal v3 To: Jason Wang Cc: "Michael S. Tsirkin" , virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org List-ID: On Mon, Sep 11, 2017 at 3:47 AM, Jason Wang wrote: > > > On 2017=E5=B9=B409=E6=9C=8810=E6=97=A5 13:06, Michael S. Tsirkin wrote: >> >> This is an update from v2 version. >> Changes: >> - update event suppression mechanism >> - add wrap counter: DESC_WRAP flag in addition to >> DESC_DRIVER flag used for validity so device does not have to >> write out all used descriptors. > > > Do we have benchmark result to show the advantage of DESC_DRIVER over e.g > avail/used index? The KVM forum presentation has some numbers. I'm not sure that synthetic benchmarks will provide much value, as we understand the trade-off quite well. The benefit of this model is improved best case performance, by having a single cacheline read instead of two for the indirect used/avail ring mod= el. The drawback is worse worst case, as scanning the ring of descriptors introduces more cacheline misses than scanning the compressed used/avail ring. This model is easier to implement in hardware and the common case is likely close to the best case, so I think it makes sense. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org