Thu, Jun 06, 2024 at 06:25:15AM CEST, jasow...@redhat.com wrote: >On Thu, Jun 6, 2024 at 10:59 AM Jason Xing <kerneljasonx...@gmail.com> wrote: >> >> Hello Jason, >> >> On Thu, Jun 6, 2024 at 8:21 AM Jason Wang <jasow...@redhat.com> wrote: >> > >> > On Wed, Jun 5, 2024 at 7:51 PM Heng Qi <hen...@linux.alibaba.com> wrote: >> > > >> > > On Wed, 5 Jun 2024 13:30:51 +0200, Jiri Pirko <j...@resnulli.us> wrote: >> > > > Mon, May 20, 2024 at 02:48:15PM CEST, j...@resnulli.us wrote: >> > > > >Fri, May 10, 2024 at 09:11:16AM CEST, hen...@linux.alibaba.com wrote: >> > > > >>On Thu, 9 May 2024 13:46:15 +0200, Jiri Pirko <j...@resnulli.us> >> > > > >>wrote: >> > > > >>> From: Jiri Pirko <j...@nvidia.com> >> > > > >>> >> > > > >>> Add support for Byte Queue Limits (BQL). >> > > > >> >> > > > >>Historically both Jason and Michael have attempted to support BQL >> > > > >>for virtio-net, for example: >> > > > >> >> > > > >>https://lore.kernel.org/netdev/21384cb5-99a6-7431-1039-b356521e1...@redhat.com/ >> > > > >> >> > > > >>These discussions focus primarily on: >> > > > >> >> > > > >>1. BQL is based on napi tx. Therefore, the transfer of statistical >> > > > >>information >> > > > >>needs to rely on the judgment of use_napi. When the napi mode is >> > > > >>switched to >> > > > >>orphan, some statistical information will be lost, resulting in >> > > > >>temporary >> > > > >>inaccuracy in BQL. >> > > > >> >> > > > >>2. If tx dim is supported, orphan mode may be removed and tx irq >> > > > >>will be more >> > > > >>reasonable. This provides good support for BQL. >> > > > > >> > > > >But when the device does not support dim, the orphan mode is still >> > > > >needed, isn't it? >> > > > >> > > > Heng, is my assuption correct here? Thanks! >> > > > >> > > >> > > Maybe, according to our cloud data, napi_tx=on works better than orphan >> > > mode in >> > > most scenarios. Although orphan mode performs better in specific >> > > benckmark, >> > >> > For example pktgen (I meant even if the orphan mode can break pktgen, >> > it can finish when there's a new packet that needs to be sent after >> > pktgen is completed). >> > >> > > perf of napi_tx can be enhanced through tx dim. Then, there is no reason >> > > not to >> > > support dim for devices that want the best performance. >> > >> > Ideally, if we can drop orphan mode, everything would be simplified. >> >> Please please don't do this. Orphan mode still has its merits. In some >> cases which can hardly be reproduced in production, we still choose to >> turn off the napi_tx mode because the delay of freeing a skb could >> cause lower performance in the tx path, > >Well, it's probably just a side effect and it depends on how to define >performance here. > >> which is, I know, surely >> designed on purpose. > >I don't think so and no modern NIC uses that. It breaks a lot of things. > >> >> If the codes of orphan mode don't have an impact when you enable >> napi_tx mode, please keep it if you can. > >For example, it complicates BQL implementation.
Well, bql could be disabled when napi is not used. It is just a matter of one "if" in the xmit path. > >Thanks > >> >> Thank you. >> >
