Re: [PATCH net-next v2 1/4] eth: mpnic: count packets, bytes, and drops per ring

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-10-20 14:50:38 [-0700], Jakub Kicinski wrote:
> On Tue, 20 Oct 2026 23:21:55 +0200 Sebastian Andrzej Siewior wrote:
> > > > Is there any other driver doing this?
> > > > There is ::get_sset_count() and so on for the per-queue stats.  
> > > 
> > > You may be mixing up queue stats (netlink) with the old ethtool -S
> > > kitchen sink / garbage dump.  
> > 
> > The statistics is folded on device-down into a global counter. So on
> > device-up the statistics is still available. At least that is my
> > understanding. This means the per-queue stats are lost and global stats
> > don't match the per queue stats anymore.
> 
> Yes, that's intentional and recommended by the docs for queue stats.

I guess this is Documentation/networking/statistics.rst that I need to
study.

> > So if this never happens, it might not be needed to preserve this. That
> > force-RCU might not be needed. This does happen on down and I would
> > assume that the device is no longer processing packets.
> 
> The (old) ndo for stats reading runs under RCU, only.
> AI will immediately point that out if we remove the sync.
> 
> May I ask why you care? Is there another driver you're trying 
> to implement stats in? I'm not sure where you're coming from
> and therefore what to explain to you.

I tried to be useful and do so some reviews and this stats part is what
I did not expect to be "expected". I would expect per-queue stats which
are folded into device stats on query time. Anyway. Let me study what is
recommended before making noise here again.
One last thing: If you replace RCU with SRCU then the logic should
remain the same. On the plus side you would have some domain separation
and the "synchronize" part will not force/ wait for the global grace
period but be limited to the local one.

Sebastian