> From: Michael S. Tsirkin <m...@redhat.com>
> Sent: Sunday, February 4, 2024 6:40 AM
> To: Jason Wang <jasow...@redhat.com>
> Cc: Jakub Kicinski <k...@kernel.org>; Jason Xing
> <kerneljasonx...@gmail.com>; Daniel Jurgens <dani...@nvidia.com>;
> netdev@vger.kernel.org; xuanz...@linux.alibaba.com;
> virtualizat...@lists.linux.dev; da...@davemloft.net;
> eduma...@google.com; ab...@redhat.com; Parav Pandit
> <pa...@nvidia.com>
> 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 <k...@kernel.org> 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-lei...@debian.or
> > > 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.
