On Mon, Feb 05, 2024 at 09:45:38AM +0800, Jason Wang wrote: > On Sun, Feb 4, 2024 at 8:39 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > On Sun, Feb 04, 2024 at 09:20:18AM +0800, Jason Wang wrote: > > > On Sat, Feb 3, 2024 at 12:01 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > > > > > > > On Fri, 2 Feb 2024 14:52:59 +0800 Jason Xing wrote: > > > > > > Can you say more? I'm curious what's your use case. > > > > > > > > > > I'm not working at Nvidia, so my point of view may differ from theirs. > > > > > From what I can tell is that those two counters help me narrow down > > > > > the range if I have to diagnose/debug some issues. > > > > > > > > right, i'm asking to collect useful debugging tricks, nothing against > > > > the patch itself :) > > > > > > > > > 1) I sometimes notice that if some irq is held too long (say, one > > > > > simple case: output of printk printed to the console), those two > > > > > counters can reflect the issue. > > > > > 2) Similarly in virtio net, recently I traced such counters the > > > > > current kernel does not have and it turned out that one of the output > > > > > queues in the backend behaves badly. > > > > > ... > > > > > > > > > > Stop/wake queue counters may not show directly the root cause of the > > > > > issue, but help us 'guess' to some extent. > > > > > > > > I'm surprised you say you can detect stall-related issues with this. > > > > I guess virtio doesn't have BQL support, which makes it special. > > > > > > Yes, virtio-net has a legacy orphan mode, this is something that needs > > > to be dropped in the future. This would make BQL much more easier to > > > be implemented. > > > > > > It's not that we can't implement BQL, > > Well, I don't say we can't, I say it's not easy as we need to deal > with the switching between two modes[1]. If we just have one mode like > TX interrupt, we don't need to care about that. > > > it's that it does not seem to > > be benefitial - has been discussed many times. > > Virtio doesn't differ from other NIC too much, for example gve supports bql. > > 1) There's no numbers in [1] > 2) We only benchmark vhost-net but not others, for example, vhost-user > and hardware implementations > 3) We don't have interrupt coalescing in 2018 but now we have with DIM Only works well with hardware virtio cards though. > Thanks > > [1] https://lore.kernel.org/netdev/20181205225323.12555-1-mst@xxxxxxxxxx/ > So fundamentally, someone needs to show benefit and no serious regressions to add BQL at this point. I doubt it's easily practical. Hacks like wireless does to boost buffer sizes might be necessary. > > > > > > Normal HW drivers with BQL almost never stop the queue by themselves. > > > > I mean - if they do, and BQL is active, then the system is probably > > > > misconfigured (queue is too short). This is what we use at Meta to > > > > detect stalls in drivers with BQL: > > > > > > > > https://lore.kernel.org/all/20240131102150.728960-3-leitao@xxxxxxxxxx/ > > > > > > > > Daniel, I think this may be a good enough excuse to add per-queue stats > > > > to the netdev genl family, if you're up for that. LMK if you want more > > > > info, otherwise I guess ethtool -S is fine for now. > > > > > > > > > > Thanks > >
