> From: Michael S. Tsirkin <mst@xxxxxxxxxx> > Sent: Sunday, February 4, 2024 6:40 AM > To: Jason Wang <jasowang@xxxxxxxxxx> > Cc: Jakub Kicinski <kuba@xxxxxxxxxx>; Jason Xing > <kerneljasonxing@xxxxxxxxx>; Daniel Jurgens <danielj@xxxxxxxxxx>; > netdev@xxxxxxxxxxxxxxx; xuanzhuo@xxxxxxxxxxxxxxxxx; > virtualization@xxxxxxxxxxxxxxx; davem@xxxxxxxxxxxxx; > edumazet@xxxxxxxxxx; abeni@xxxxxxxxxx; Parav Pandit > <parav@xxxxxxxxxx> > Subject: Re: [PATCH net-next] virtio_net: Add TX stop and wake counters > > 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, it's that it does not seem to be > benefitial - has been discussed many times. > > > > 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@xxxxxxxxx > > > g/ > > > > > > 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 Michael, Are you OK with this patch? Unless I missed it I didn't see a response from you in our conversation the day I sent it.
