On Fri, Jun 07, 2024 at 02:22:31PM +0800, Jason Wang wrote: > On Thu, Jun 6, 2024 at 9:41 PM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > > > > Thu, Jun 06, 2024 at 06:25:15AM CEST, jasowang@xxxxxxxxxx wrote: > > >On Thu, Jun 6, 2024 at 10:59 AM Jason Xing <kerneljasonxing@xxxxxxxxx> wrote: > > >> > > >> Hello Jason, > > >> > > >> On Thu, Jun 6, 2024 at 8:21 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > >> > > > >> > On Wed, Jun 5, 2024 at 7:51 PM Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> wrote: > > >> > > > > >> > > On Wed, 5 Jun 2024 13:30:51 +0200, Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > > >> > > > Mon, May 20, 2024 at 02:48:15PM CEST, jiri@xxxxxxxxxxx wrote: > > >> > > > >Fri, May 10, 2024 at 09:11:16AM CEST, hengqi@xxxxxxxxxxxxxxxxx wrote: > > >> > > > >>On Thu, 9 May 2024 13:46:15 +0200, Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > > >> > > > >>> From: Jiri Pirko <jiri@xxxxxxxxxx> > > >> > > > >>> > > >> > > > >>> 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-b356521e1bc3@xxxxxxxxxx/ > > >> > > > >> > > >> > > > >>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. > > Maybe, care to post a patch? > > The trick part is, a skb is queued when BQL is enabled but sent when > BQL is disabled as discussed here: > > https://lore.kernel.org/netdev/21384cb5-99a6-7431-1039-b356521e1bc3@xxxxxxxxxx/ > > Thanks Yes of course. Or we can stick a dummy value in skb->destructor after we orphan, maybe that's easier. > > > > > > > > > >Thanks > > > > > >> > > >> Thank you. > > >> > > > > >
