netdev - Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount

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Message-ID: <1490027684.16816.63.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Mon, 20 Mar 2017 09:34:44 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>, elena.reshetova@...el.com,
        keescook@...omium.org, netdev@...r.kernel.org,
        bridge@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kuznet@....inr.ac.ru, jmorris@...ei.org, kaber@...sh.net,
        stephen@...workplumber.org, ishkamiel@...il.com,
        dwindsor@...il.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to
 refcount_t

On Mon, 2017-03-20 at 09:18 -0700, Eric Dumazet wrote:

> Interesting.
> 
> UDP ipv4 xmit path gets a ~25 % improvement on PPC with this patch.
> 
> ( 20 concurrent netperf -t UDP_STREAM  : 2.45 Mpps -> 3.07 Mpps )

Well, there _is_ a difference, but not 25 % (this was probably caused by
different queues on TX or RX between my reboots).

I added a sysctl hack to be able to dynamically change on a given
workload, and we hit other bottlenecks (mainly qdisc locks and driver tx
locks) anyway.