From: Jakub Kicinski <kuba@kernel.org>
Sent: Friday, February 2, 2024 10:01 AM
Subject: Re: [PATCH net-next] virtio_net: Add TX stop and wake counters

On Fri, 2 Feb 2024 14:52:59 +0800 Jason Xing wrote:

quoted

quoted

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 :)

quoted

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.
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@debian.org/ (local)

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.

For now, I would like to go with ethtool -S. But I can take on the netdev level as a background task. Are you suggesting adding them to rtnl_link_stats64?