From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-5458-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 058249812AE for ; Tue, 19 Feb 2019 14:18:21 +0000 (UTC) Date: Tue, 19 Feb 2019 09:18:16 -0500 From: "Michael S. Tsirkin" Message-ID: <20190219091733-mutt-send-email-mst@kernel.org> References: <20190211233612-mutt-send-email-mst@kernel.org> <3ce6415d-e36d-8dcb-dd99-5203a63e5883@redhat.com> <20190212082915-mutt-send-email-mst@kernel.org> <9bed9f5d-ab7d-287e-3497-0c4b61e3b8c0@redhat.com> <20190213100640-mutt-send-email-mst@kernel.org> <20190213223515-mutt-send-email-mst@kernel.org> <8106d176-5560-7a1b-1e4d-b8f0033ae461@redhat.com> <20190214231127-mutt-send-email-mst@kernel.org> <93a9569e-03d3-b1ad-e0d7-96287870b6b5@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <93a9569e-03d3-b1ad-e0d7-96287870b6b5@redhat.com> Subject: Re: [virtio-dev] RFC: Doorbell suppression, packed-ring mode and hardware offload To: Jason Wang Cc: David Riddoch , Virtio-Dev List-ID: On Tue, Feb 19, 2019 at 02:21:01PM +0800, Jason Wang wrote: > > On 2019/2/15 下午12:23, Michael S. Tsirkin wrote: > > On Fri, Feb 15, 2019 at 11:59:55AM +0800, Jason Wang wrote: > > > On 2019/2/14 上午11:41, Michael S. Tsirkin wrote: > > > > > I think it's as simple as increase the avail idx by X? Since descriptor were > > > > > used in order, device can just read the next X-1 descriptors in this case. > > > > > > > > > > Thanks > > > > Right so a spec change would be needed, it's not transparent to guest. > > > > > > With the change, IN_ORDER + split_ring becomes something like submission > > > queue (descriptor ring) + completion queue (used ring). And used ring access > > > could be eliminated sometime, e.g for net for TX, we don't care about used > > > len. > > Oh yes but fundamentally this becomes very close to packed ring. > > > Looks not, it's a two rings vs one ring. > > > > So I'm > > not sure yet another option is justified by a small gain in PPS, > > > 10% is done with less than 10 lines of code, I suspect maybe dpdk can see > more. > > > > especially considering that it depends on in order and so doesn't > > support zero copy. > > > It looks to me in order is not the blocker, even if we allow out of order, > we may still suffer from HOL. HOL isn't an issue with e.g. a dedicated VF. > > > > > > What's more interesting is, this avail idx optimization is not required for > > > out of order completion which means it could be used for e.g block or SCSI > > > device. > > I don't get the last sentence. This only works for in order right? > > > Yes, you are right. > > Thanks. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org