> From: Michael S. Tsirkin <m...@redhat.com>
> Sent: Wednesday, February 7, 2024 2:19 PM
> To: Daniel Jurgens <dani...@nvidia.com>
> Subject: Re: [PATCH net-next] virtio_net: Add TX stop and wake counters
> 
> On Wed, Feb 07, 2024 at 07:38:16PM +0000, Daniel Jurgens wrote:
> > > 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-leitao@debia
> > > > > n.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.
> >
> 
> I thought what is proposed is adding some support for these stats to core?
> Did I misunderstood?
> 

That's a much bigger change and going that route I think still need to count 
them at the driver level. I said I could potentially take that on as a 
background project. But would prefer to go with ethtool -S for now.

> --
> MST

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