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Tsirkin" , Heng Qi Cc: Halil Pasic , virtio-comment@lists.linux.dev, Jason Wang , Parav Pandit , Xuan Zhuo Subject: Re: [PATCH v5] virtio-net: clarify coalescing parameters settings In-Reply-To: <20240610104618-mutt-send-email-mst@kernel.org> Organization: "Red Hat GmbH, Sitz: Werner-von-Siemens-Ring 12, D-85630 Grasbrunn, Handelsregister: Amtsgericht =?utf-8?Q?M=C3=BCnchen=2C?= HRB 153243, =?utf-8?Q?Gesch=C3=A4ftsf=C3=BChrer=3A?= Ryan Barnhart, Charles Cachera, Michael O'Neill, Amy Ross" References: <20240528044702.50603-1-hengqi@linux.alibaba.com> <20240607220246.3213607c.pasic@linux.ibm.com> <1717814062.4461155-1-hengqi@linux.alibaba.com> <20240610144602.57a04723.pasic@linux.ibm.com> <1718026545.7557275-2-hengqi@linux.alibaba.com> <20240610104618-mutt-send-email-mst@kernel.org> User-Agent: Notmuch/0.38.3 (https://notmuchmail.org) Date: Tue, 11 Jun 2024 16:04:01 +0200 Message-ID: <87tthzk23y.fsf@redhat.com> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain On Mon, Jun 10 2024, "Michael S. Tsirkin" wrote: > On Mon, Jun 10, 2024 at 09:35:45PM +0800, Heng Qi wrote: >> On Mon, 10 Jun 2024 14:46:02 +0200, Halil Pasic wrote: >> > On Sat, 8 Jun 2024 10:34:22 +0800 >> > Heng Qi wrote: >> > >> > > On Fri, 7 Jun 2024 22:02:46 +0200, Halil Pasic wrote: >> > > > On Tue, 28 May 2024 12:47:02 +0800 >> > > > Heng Qi wrote: >> > > > >> > > > > The device can set any initial coalescing parameters (0 or non-zero) >> > > > > for the receive/send queue before the setting command is executed, >> > > > > not just 0, enhancing device performance even without DIM enabled. >> > > > > >> > > > > So we need to clarify descriptions that don't fit the behavior. >> > > > >> > > > Sorry I'm late to the party -- again! Just for my understanding: how/why >> > > > is this a clarification and not just a (basically incompatible) change? >> > > >> > > In my opinion, "clarification" means that something may have been described >> > > incorrectly before, and we now need to discuss, explain clearly, and correct >> > > the possibly incorrect description. >> > > >> > >> > I figure the difference in perceived semantics of the word >> > "clarification" is at the root of my confusion. Let us have a look at >> > https://dictionary.cambridge.org/de/worterbuch/englisch/clarification >> > >> > According to my understanding a "clarification", while an improvement in >> > ease of understanding and/or decrease of ambiguity (possibly to no >> > ambiguity at all) implies that what receiving a clarification is not >> > outright wrong. >> > >> > When rectifying something that is outright incorrect or wrong, I would >> > refer to that with words like "correction", "fix", "erratum" or >> > "corrigendum". >> > >> > > > >> > > > I mean if I read this correctly, before the driver had the guaranty >> > > > that if the parameters are not set by the driver, negotiating the >> > > > feature does not introduce any coalescing. After this in theory >> > > > the device could just pick some max value and potentially introduce >> > > > maximal latency in certain scenarios. >> > > >> > > "maximum latency" also means "throughput improvement". >> > > >> > >> > Under certain assumptions. But not necessarily. Again my concern is >> > mostly the type of change. The virtio standard maintain a revision >> > history appendix, and I would like to avoid the nature of this change >> > being misrepresented there. If Connie and/or Michael think it is worth >> > fixing, I believe it can be fixed with an editorial change. >> > >> > AFAIU VIRTIO_NET_F_NOTF_COAL and VIRTIO_NET_F_VQ_NOTF_COAL are about to >> > land with virtio-1.3, i.e. there is no released/standardized virtio >> > version where the "initialize to 0" is released. In that sense it looks >> > like we are still on time to change this. But I am not 100% certain. In >> > any case I don't think this as a huge impact and I'm fine going ahead >> > with the change. >> >> Sorry for the late reply, I'm on vacation. >> >> I agree with this, and I prefer to release this patch as a correction for >> virtio1.3 instead of a new patch for virtio1.4, because if devices support moderation coalescing based on virtio1.3, >> and after virtio1.4 is released, these devices need to be updated again for a >> more reasonable coalescing parameters. >> >> Cornelia and Michael, what do you think? > > The TC is just voting to start the public review process. > We can defer that by a couple more weeks if there is > a known issue to address. > > For that I expect we want a final patch and a couple of acks > on list from TC members by end of the ballot, June 13. FTR, I'd be fine with that if there's a consensus, but I'll not be around to handle this personally. I also have no objection to proceeding with the process.