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

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Date:   Tue, 10 Dec 2019 22:52:59 +0200
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Vivien Didelot <vivien.didelot@...il.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 10/12/2019 22:34, Vivien Didelot wrote:
> On Tue, 10 Dec 2019 22:15:26 +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.
> 
> 
> Thanks,
> 
> 	Vivien
> 

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.

Cheers,
 Nik