netdev - Re: [PATCH net-next v2 1/1] driver: veth: Refine the statistics codes of veth driver

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Date:   Thu, 3 Nov 2016 21:39:11 +0800
From:   Gao Feng <fgao@...ai8.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Cong Wang <cwang@...pensource.com>,
        Vijay Pandurangan <vijayp@...ayp.ca>,
        Evan Jones <ej@...njones.ca>, pabeni@...hat.com,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 1/1] driver: veth: Refine the statistics codes
 of veth driver

Hi Eric,

On Thu, Nov 3, 2016 at 9:30 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2016-11-03 at 21:03 +0800, fgao@...ai8.com wrote:
>> From: Gao Feng <fgao@...ai8.com>
>>
>> The dropped count of veth is located in struct veth_priv, but other
>> statistics like packets and bytes are in another struct pcpu_vstats.
>> Now keep these three counters in the same struct.
>>
>> Signed-off-by: Gao Feng <fgao@...ai8.com>
>> ---
>>  v2: Use right "peer" instead of "dev";
>>  v1: Initial version
>
> May I ask : Why ?

Just because I think statistics should be in the same struct.

>
> We did that because there was no point making per-cpu requirements
> bigger, for a counter that is hardly ever updated.
>
> Do you have a real case where performance dropping packets in a driver
> is needed ?

No, I haven't met the performance issue now.

>
> At some point we will have to stop dumb percpu explosion, when we have
> 128+ cores per host. Folding all these percpu counters is taking a lot
> of time too.
>
>
>
Ok, I get it. It is designed specially to put the dropped counter as
atomic counter, not percpu.
But I have one question that when put the counters as percpu, and when not?

Regards
Feng