netdev - Re: [PATCH net-next] virtio_net: Add TX stop and wake counters

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Message-ID: <CAL+tcoCs6x7=rBj50g2cMjwLjLOKs9xy1ZZBwSQs8bLfzm=B7Q@mail.gmail.com>
Date: Fri, 2 Feb 2024 14:52:59 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Daniel Jurgens <danielj@...dia.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "jasowang@...hat.com" <jasowang@...hat.com>, 
	"xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>, 
	"virtualization@...ts.linux.dev" <virtualization@...ts.linux.dev>, 
	"davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>, 
	"abeni@...hat.com" <abeni@...hat.com>, Parav Pandit <parav@...dia.com>
Subject: Re: [PATCH net-next] virtio_net: Add TX stop and wake counters

On Fri, Feb 2, 2024 at 12:21 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 31 Jan 2024 10:54:33 +0800 Jason Xing wrote:
> > > [danielj@...mtx-051 upstream]$ ethtool -S ens2f1np1 | grep 'stop\|wake'
> > >      tx_queue_stopped: 0
> > >      tx_queue_wake: 0
> > >      tx0_stopped: 0
> > >      tx0_wake: 0
> > >      ....
> >
> > Yes, that's it! What I know is that only mlx drivers have those two
> > counters, but they are very useful when debugging some issues or
> > tracking some historical changes if we want to.
>
> 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.
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.

Thanks,
Jason