> From: Michael S. Tsirkin <mst@xxxxxxxxxx> > Sent: Wednesday, February 7, 2024 2:19 PM > To: Daniel Jurgens <danielj@xxxxxxxxxx> > 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 <mst@xxxxxxxxxx> > > > Sent: Sunday, February 4, 2024 6:40 AM > > > To: Jason Wang <jasowang@xxxxxxxxxx> > > > Cc: Jakub Kicinski <kuba@xxxxxxxxxx>; Jason Xing > > > <kerneljasonxing@xxxxxxxxx>; Daniel Jurgens <danielj@xxxxxxxxxx>; > > > netdev@xxxxxxxxxxxxxxx; xuanzhuo@xxxxxxxxxxxxxxxxx; > > > virtualization@xxxxxxxxxxxxxxx; davem@xxxxxxxxxxxxx; > > > edumazet@xxxxxxxxxx; abeni@xxxxxxxxxx; Parav Pandit > > > <parav@xxxxxxxxxx> > > > 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@xxxxxxxxxx> > 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
