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

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Message-ID: <1490194444.16816.154.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 22 Mar 2017 07:54:04 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
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, 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.

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.