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Date: Wed, 22 Mar 2017 13:11:00 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Kees Cook <keescook@...omium.org> Cc: Eric Dumazet <eric.dumazet@...il.com>, 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 Tue, Mar 21, 2017 at 04:51:13PM -0700, Kees Cook wrote: > On Tue, Mar 21, 2017 at 2:23 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > > Unfortunately there is no good test simulating real-world workloads, > > which are mostly using TCP flows. > > Sure, but there has to be _something_ that can be used to test to > measure the effects. Without a meaningful test, it's weird to reject a > change for performance reasons. This. How can you optimize if there's no way to actually measure something? > > Most synthetic tools you can find are not using epoll(), and very often > > hit bottlenecks in other layers. > > > > > > It looks like our suggestion to get kernel builds with atomic_inc() > > being exactly an atomic_inc() is not even discussed or implemented. > > So, FWIW, I originally tried to make this a CONFIG in the first couple > passes at getting a refcount defense. I would be fine with this, but I > was not able to convince Peter. :) However, things have evolved a lot > since then, so perhaps there are things do be done here. Well, the argument was that unless there's a benchmark that shows it cares, its all premature optimization. Similarly, you wanted this enabled at all times because hardening.
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