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

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Message-ID: <1478179858.7065.438.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 03 Nov 2016 06:30:58 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     fgao@...ai8.com
Cc:     davem@...emloft.net, cwang@...pensource.com, vijayp@...ayp.ca,
        ej@...njones.ca, pabeni@...hat.com, netdev@...r.kernel.org,
        gfree.wind@...il.com
Subject: Re: [PATCH net-next v2 1/1] driver: veth: Refine the statistics
 codes of veth driver

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 ?

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 ?

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.