netdev - Re: [PATCH net-next] net: bridge: add STP xstats

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Date:   Tue, 10 Dec 2019 16:08:36 -0500
From:   Vivien Didelot <vivien.didelot@...il.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net-next] net: bridge: add STP xstats

On Tue, 10 Dec 2019 22:52:59 +0200, Nikolay Aleksandrov <nikolay@...ulusnetworks.com> wrote:
> >>>>>> Why do you need percpu ? All of these seem to be incremented with the
> >>>>>> bridge lock held. A few more comments below.
> >>>>>
> >>>>> All other xstats are incremented percpu, I simply followed the pattern.
> >>>>>
> >>>>
> >>>> We have already a lock, we can use it and avoid the whole per-cpu memory handling.
> >>>> It seems to be acquired in all cases where these counters need to be changed.
> >>>
> >>> Since the other xstats counters are currently implemented this way, I prefer
> >>> to keep the code as is, until we eventually change them all if percpu is in
> >>> fact not needed anymore.
> >>>
> >>> The new series is ready and I can submit it now if there's no objection.
> >>
> >> There is a reason other counters use per-cpu - they're incremented without any locking from fast-path.
> >> The bridge STP code already has a lock which is acquired in all of these paths and we don't need
> >> this overhead and the per-cpu memory allocations. Unless you can find a STP codepath which actually
> >> needs per-cpu, I'd prefer you drop it.
> > 
> > Ho ok I understand what you mean now. I'll drop the percpu attribute.
> 
> Great, thanks again.
> I think it's clear, but I'll add just in case to avoid extra work - you can drop
> the dynamic memory allocation altogether and make the struct part of net_bridge_port.

Yup, that's what I've done and it makes the patch shamely small now ;)


Thanks,

	Vivien