Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933607AbdCUX6D (ORCPT ); Tue, 21 Mar 2017 19:58:03 -0400 Received: from mail-io0-f175.google.com ([209.85.223.175]:34148 "EHLO mail-io0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933403AbdCUX57 (ORCPT ); Tue, 21 Mar 2017 19:57:59 -0400 MIME-Version: 1.0 In-Reply-To: <1490131389.16816.123.camel@edumazet-glaptop3.roam.corp.google.com> References: <1489767196.28631.305.camel@edumazet-glaptop3.roam.corp.google.com> <20170318164759.GA23837@gondor.apana.org.au> <20170318.182121.439615057765380575.davem@davemloft.net> <20170320103937.lq7nfnutupr3gkn7@hirez.programming.kicks-ass.net> <20170320131629.GA26405@gondor.apana.org.au> <20170320132357.acygo3umw6fiwb4p@hirez.programming.kicks-ass.net> <20170320132713.GA26954@gondor.apana.org.au> <20170320134017.h3c2jrsnd4guuyu7@hirez.programming.kicks-ass.net> <1490131389.16816.123.camel@edumazet-glaptop3.roam.corp.google.com> From: Kees Cook Date: Tue, 21 Mar 2017 16:51:13 -0700 X-Google-Sender-Auth: WBsNfsZnYTtAIGr2WbVJ6madVZA Message-ID: Subject: Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t To: Eric Dumazet Cc: Peter Zijlstra , Herbert Xu , David Miller , "Reshetova, Elena" , Network Development , bridge@lists.linux-foundation.org, LKML , Alexey Kuznetsov , James Morris , Patrick McHardy , Stephen Hemminger , Hans Liljestrand , David Windsor , Andrew Morton Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2060 Lines: 66 On Tue, Mar 21, 2017 at 2:23 PM, Eric Dumazet wrote: > On Tue, 2017-03-21 at 13:49 -0700, Kees Cook wrote: > >> Yeah, this is exactly what I'd like to find as well. Just comparing >> cycles between refcount implementations, while interesting, doesn't >> show us real-world performance changes, which is what we need to >> measure. >> >> Is Eric's "20 concurrent 'netperf -t UDP_STREAM'" example (from >> elsewhere in this email thread) real-world meaningful enough? > > Not at all ;) > > This was targeting the specific change I had in mind for > ip_idents_reserve(), which is not used by TCP flows. Okay, I just wanted to check. I didn't think so, but it was the only example in the thread. > 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. > 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. > Coding this would require less time than running a typical Google kernel > qualification (roughly one month, thousands of hosts..., days of SWE). It wasn't the issue of coding time; just that it had been specifically not wanted. :) Am I understanding you correctly that you'd want something like: refcount.h: #ifdef UNPROTECTED_REFCOUNT #define refcount_inc(x) atomic_inc(x) ... #else void refcount_inc(... ... #endif some/net.c: #define UNPROTECTED_REFCOUNT #include or similar? -Kees -- Kees Cook Pixel Security