On Fri, Jun 7, 2024 at 2:39 PM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > > Fri, Jun 07, 2024 at 08:25:19AM CEST, jasowang@xxxxxxxxxx wrote: > >On Thu, Jun 6, 2024 at 9:45 PM Jiri Pirko <jiri@xxxxxxxxxxx> wrote: > >> > >> Thu, Jun 06, 2024 at 09:56:50AM CEST, jasowang@xxxxxxxxxx wrote: > >> >On Thu, Jun 6, 2024 at 2:05 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > >> >> > >> >> On Thu, Jun 06, 2024 at 12:25:15PM +0800, Jason Wang wrote: > >> >> > > 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. > >> >> > > >> >> > Thanks > >> >> > >> >> I very much doubt sending interrupts to a VM can > >> >> *on all benchmarks* compete with not sending interrupts. > >> > > >> >It should not differ too much from the physical NIC. We can have one > >> >more round of benchmarks to see the difference. > >> > > >> >But if NAPI mode needs to win all of the benchmarks in order to get > >> >rid of orphan, that would be very difficult. Considering various bugs > >> >will be fixed by dropping skb_orphan(), it would be sufficient if most > >> >of the benchmark doesn't show obvious differences. > >> > > >> >Looking at git history, there're commits that removes skb_orphan(), for example: > >> > > >> >commit 8112ec3b8722680251aecdcc23dfd81aa7af6340 > >> >Author: Eric Dumazet <edumazet@xxxxxxxxxx> > >> >Date: Fri Sep 28 07:53:26 2012 +0000 > >> > > >> > mlx4: dont orphan skbs in mlx4_en_xmit() > >> > > >> > After commit e22979d96a55d (mlx4_en: Moving to Interrupts for TX > >> > completions) we no longer need to orphan skbs in mlx4_en_xmit() > >> > since skb wont stay a long time in TX ring before their release. > >> > > >> > Orphaning skbs in ndo_start_xmit() should be avoided as much as > >> > possible, since it breaks TCP Small Queue or other flow control > >> > mechanisms (per socket limits) > >> > > >> > Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> > >> > Acked-by: Yevgeny Petrilin <yevgenyp@xxxxxxxxxxxx> > >> > Cc: Or Gerlitz <ogerlitz@xxxxxxxxxxxx> > >> > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> > >> > > >> >> > >> >> So yea, it's great if napi and hardware are advanced enough > >> >> that the default can be changed, since this way virtio > >> >> is closer to a regular nic and more or standard > >> >> infrastructure can be used. > >> >> > >> >> But dropping it will go against *no breaking userspace* rule. > >> >> Complicated? Tough. > >> > > >> >I don't know what kind of userspace is broken by this. Or why it is > >> >not broken since the day we enable NAPI mode by default. > >> > >> There is a module option that explicitly allows user to set > >> napi_tx=false > >> or > >> napi_weight=0 > >> > >> So if you remove this option or ignore it, both breaks the user > >> expectation. > > > >We can keep them, but I wonder what's the expectation of the user > >here? The only thing so far I can imagine is the performance > >difference. > > True. > > > > >> I personally would vote for this breakage. To carry ancient > >> things like this one forever does not make sense to me. > > > >Exactly. > > > >> While at it, > >> let's remove all virtio net module params. Thoughts? > > > >I tend to > > > >1) drop the orphan mode, but we can have some benchmarks first > > Any idea which? That would be really tricky to find the ones where > orphan mode makes difference I assume. True. Personally, I would like to just drop orphan mode. But I'm not sure others are happy with this. Thanks > > > >2) keep the module parameters > > and ignore them, correct? Perhaps a warning would be good. > > > > > >Thanks > > > >> > >> > >> > >> > > >> >Thanks > >> > > >> >> > >> >> -- > >> >> MST > >> >> > >> > > >> > > >
