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

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Date:   Wed, 22 Mar 2017 16:08:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        bridge@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Patrick McHardy <kaber@...sh.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to
 refcount_t

On Wed, Mar 22, 2017 at 07:54:04AM -0700, Eric Dumazet wrote:
> On Wed, 2017-03-22 at 15:33 +0100, Peter Zijlstra wrote:
> 
> > 
> > But I would feel a whole lot better about the entire thing if we could
> > measure their impact. It would also give us good precedent to whack
> > other potential users of _nocheck over the head with -- show numbers.
> 
> I wont be able to measure the impact on real workloads, our productions
> kernels are based on 4.3 at this moment.

Is there really no micro bench that exercises the relevant network
paths? Do you really fully rely on Google production workloads?

> I guess someone could code a lib/test_refcount.c launching X threads
> using either atomic_inc or refcount_inc() in a loop.
> 
> That would give a rough estimate of the refcount_t overhead among
> various platforms.

Its also a fairly meaningless number. It doesn't include any of the
other work the network path does.