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Tsirkin" , Parav Pandit , Cornelia Huck , Xuan Zhuo , Halil Pasic Subject: Re: [PATCH v5] virtio-net: clarify coalescing parameters settings Message-ID: <20240607220246.3213607c.pasic@linux.ibm.com> In-Reply-To: <20240528044702.50603-1-hengqi@linux.alibaba.com> References: <20240528044702.50603-1-hengqi@linux.alibaba.com> Organization: IBM X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 7La32Zy9TIDR_rDhQ0AVqvdIhV1Et50P X-Proofpoint-GUID: wz5hq40993dM8yvAAWV8aLnVp17FMGM_ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-06-07_12,2024-06-06_02,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 bulkscore=0 priorityscore=1501 malwarescore=0 spamscore=0 mlxlogscore=999 clxscore=1011 lowpriorityscore=0 suspectscore=0 phishscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2405010000 definitions=main-2406070147 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? 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. I understand that it is probably in the best interest of the devices to not pick stupid defaults. But it is also probably in the best interest of the driver to set those params, and if the driver is going to set its values, the devices defaults are moot unless we assume that those may end up being used by the driver as a hint when deciding which parameter values to choose. What am I missing here? Regards, Halil