On Thu, Jun 06, 2024 at 07:42:35PM +0800, Jason Xing wrote: > On Thu, Jun 6, 2024 at 12:25 PM Jason Wang <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. > > Yes. > > > > > > 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. > > To avoid confusion, I meant napi_tx mode can delay/slow down the speed > in the tx path and no modern nic uses skb_orphan().
Clearly it's been designed for software NICs and when the cost of interrupts is very high. > I think I will have some time to test BQL in virtio_net. > > Thanks, > Jason
