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[79.178.32.166]) by smtp.gmail.com with ESMTPSA id c20sm707561wmb.38.2020.12.28.13.38.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Dec 2020 13:38:36 -0800 (PST) Date: Mon, 28 Dec 2020 16:38:33 -0500 From: "Michael S. Tsirkin" To: Willem de Bruijn Cc: virtualization@lists.linux-foundation.org, Network Development , Jason Wang Subject: Re: [PATCH rfc 0/3] virtio-net: add tx-hash, rx-tstamp and tx-tstamp Message-ID: <20201228163809-mutt-send-email-mst@kernel.org> References: <20201228162233.2032571-1-willemdebruijn.kernel@gmail.com> <20201228122911-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Dec 28, 2020 at 02:51:09PM -0500, Willem de Bruijn wrote: > On Mon, Dec 28, 2020 at 12:29 PM Michael S. Tsirkin wrote: > > > > On Mon, Dec 28, 2020 at 11:22:30AM -0500, Willem de Bruijn wrote: > > > From: Willem de Bruijn > > > > > > RFC for three new features to the virtio network device: > > > > > > 1. pass tx flow hash and state to host, for routing + telemetry > > > 2. pass rx tstamp to guest, for better RTT estimation > > > 3. pass tx tstamp to host, for accurate pacing > > > > > > All three would introduce an extension to the virtio spec. > > > I assume this would require opening three ballots against v1.2 at > > > https://www.oasis-open.org/committees/ballots.php?wg_abbrev=virtio > > > > > > This RFC is to informally discuss the proposals first. > > > > > > The patchset is against v5.10. Evaluation additionally requires > > > changes to qemu and at least one back-end. I implemented preliminary > > > support in Linux vhost-net. Both patches available through github at > > > > > > https://github.com/wdebruij/linux/tree/virtio-net-txhash-1 > > > https://github.com/wdebruij/qemu/tree/virtio-net-txhash-1 > > > > Any data on what the benefits are? > > For the general method, yes. For this specific implementation, not yet. > > Swift congestion control is delay based. It won the best paper award > at SIGCOMM this year. That paper has a lot of data: > https://dl.acm.org/doi/pdf/10.1145/3387514.3406591 . Section 3.1 talks > about the different components that contribute to delay and how to > isolate them. And for the hashing part? > BBR and BBRv2 also have an explicit ProbeRTT phase as part of the design. > > The specific additional benefits for VM-based TCP depends on many > conditions, e.g., whether a vCPU is exclusively owned and pinned. But > the same reasoning should be even more applicable to this even longer > stack, especially in the worst case conditions.