From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-5448-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 A6B219860B1 for ; Fri, 15 Feb 2019 04:23:32 +0000 (UTC) Date: Thu, 14 Feb 2019 23:23:30 -0500 From: "Michael S. Tsirkin" Message-ID: <20190214231127-mutt-send-email-mst@kernel.org> References: <20190211080432-mutt-send-email-mst@kernel.org> <97e870fd-dbd5-2fed-b62c-67d24407e5cf@solarflare.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8106d176-5560-7a1b-1e4d-b8f0033ae461@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 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. So I'm not sure yet another option is justified by a small gain in PPS, especially considering that it depends on in order and so doesn't support zero copy. > 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? -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org