From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-7041-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 [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 9C524985FDB for ; Fri, 10 Apr 2020 02:40:13 +0000 (UTC) References: <20200309030251-mutt-send-email-mst@kernel.org> <20200309060238-mutt-send-email-mst@kernel.org> <20200310021729-mutt-send-email-mst@kernel.org> <89358cf3-7ce0-7b60-f4a7-2672970a635e@redhat.com> <0f43a280-5425-3a10-1312-22ea87d320ca@redhat.com> <20200409170152-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Fri, 10 Apr 2020 10:40:00 +0800 MIME-Version: 1.0 In-Reply-To: <20200409170152-mutt-send-email-mst@kernel.org> Content-Language: en-US Subject: Re: [virtio-dev] Dirty Page Tracking (DPT) Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable To: "Michael S. Tsirkin" , Eugenio Perez Martin Cc: Rob Miller , Virtio-Dev , Paolo Bonzini , Juan Quintela List-ID: On 2020/4/10 =E4=B8=8A=E5=8D=885:06, Michael S. Tsirkin wrote: > On Tue, Apr 07, 2020 at 11:52:46AM +0200, Eugenio Perez Martin wrote: >> Hi! >> >> So, from the previous mails, it seems that monitoring the used ring >> (and the packed descriptors) is a good first step in that direction, >> as DPDK did. This way, the device does not need to worry about the >> dirty page tracking using a bitmap and the PCI writes limitation, and >> we can evaluate later the proposed alternatives: >> * Alternate used descriptors in packed. >> * vDPA interface for vDPA devices in a convenient format. >> >> Any thoughts? Do you think that we should start with another way? >> >> Thanks! > I am concerned that with software in data path, we'll hit RX queue > underruns, won't we? Do you mean it will lose some performance? If yes, I think so. > Two ways to avoid underruns: > - dirty page tracking > - page faults It looks to me this will lead even worse performance than software path?=20 There will be lots of page faults during RX. Another direction is to track dirty pages via IOMMU. E.g recent Intel=20 IOMMU has EA and D bit which could be used for tracking pages wrote by=20 devices but not CPU. > > I'm working on a proposal for page faults now. I guess it's better to have a transport independent method. > If someone wants > to work on dirty tracking in addition, that's also an option. I remember Rob mention some challenges of implementing dirty bitmap, I=20 wonder something like queue based interface would be better (similar to=20 Peter did for KVM)? Thanks --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org