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

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Message-ID:
 <CH0PR12MB85804D451A889448D3427132C9FB2@CH0PR12MB8580.namprd12.prod.outlook.com>
Date: Fri, 7 Jun 2024 12:36:58 +0000
From: Dan Jurgens <danielj@...dia.com>
To: Jason Xing <kerneljasonxing@...il.com>
CC: Jakub Kicinski <kuba@...nel.org>, "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

> From: Jason Xing <kerneljasonxing@...il.com>
> Sent: Friday, June 7, 2024 4:16 AM
> To: Dan Jurgens <danielj@...dia.com>
> Cc: Jakub Kicinski <kuba@...nel.org>; Michael S. Tsirkin <mst@...hat.com>;
> netdev@...r.kernel.org; jasowang@...hat.com;
> xuanzhuo@...ux.alibaba.com; virtualization@...ts.linux.dev;
> davem@...emloft.net; edumazet@...gle.com; abeni@...hat.com; Parav
> Pandit <parav@...dia.com>
> Subject: Re: [PATCH net-next] virtio_net: Add TX stop and wake counters
> 
> On Sat, Feb 3, 2024 at 12:46 AM Daniel Jurgens <danielj@...dia.com> wrote:
> >
> > > From: Jakub Kicinski <kuba@...nel.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:
> > > > > 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.
> > > 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.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.
> >
> > 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?
> 
> Hello Daniel, Jakub,
> 
> Sorry to revive this thread. I wonder why not use this patch like mlnx driver
> does instead of adding statistics into the yaml file? Are we gradually using or
> adding more fields into the yaml file to replace the 'ethtool -S' command?
> 

It's trivial to have the stats in ethtool as well. But I noticed the stats series intentionally removed some stats from ethtool. So I didn't put it both places.

> Thanks,
> Jason