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

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Message-ID:
 <CH0PR12MB8580F1E450D06925BEB45D72C9452@CH0PR12MB8580.namprd12.prod.outlook.com>
Date: Wed, 7 Feb 2024 19:38:16 +0000
From: Daniel Jurgens <danielj@...dia.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>
CC: Jakub Kicinski <kuba@...nel.org>, Jason Xing <kerneljasonxing@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"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: Michael S. Tsirkin <mst@...hat.com>
> Sent: Sunday, February 4, 2024 6:40 AM
> To: Jason Wang <jasowang@...hat.com>
> Cc: Jakub Kicinski <kuba@...nel.org>; Jason Xing
> <kerneljasonxing@...il.com>; Daniel Jurgens <danielj@...dia.com>;
> netdev@...r.kernel.org; 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 Sun, Feb 04, 2024 at 09:20:18AM +0800, Jason Wang wrote:
> > On Sat, Feb 3, 2024 at 12:01 AM Jakub Kicinski <kuba@...nel.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@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.