From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754793AbdC1J5B (ORCPT ); Tue, 28 Mar 2017 05:57:01 -0400 Received: from mail-vk0-f54.google.com ([209.85.213.54]:36724 "EHLO mail-vk0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754108AbdC1J47 (ORCPT ); Tue, 28 Mar 2017 05:56:59 -0400 MIME-Version: 1.0 In-Reply-To: <20170328095151.GC30567@gmail.com> References: <6bb1c71b87b300d04977c34f0cd8586363bc6170.1489519233.git.dvyukov@google.com> <20170324065203.GA5229@gmail.com> <20170324105700.GB20282@gmail.com> <20170328075232.GA19590@gmail.com> <20170328092712.bk32k5iteqqm6pgh@hirez.programming.kicks-ass.net> <20170328095151.GC30567@gmail.com> From: Dmitry Vyukov Date: Tue, 28 Mar 2017 11:56:32 +0200 Message-ID: Subject: Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations To: Ingo Molnar Cc: Peter Zijlstra , Mark Rutland , Andrey Ryabinin , Ingo Molnar , Will Deacon , Andrew Morton , kasan-dev , "linux-mm@kvack.org" , "x86@kernel.org" , LKML , Linus Torvalds , Thomas Gleixner , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 28, 2017 at 11:51 AM, Ingo Molnar wrote: > > * Peter Zijlstra wrote: > >> On Tue, Mar 28, 2017 at 09:52:32AM +0200, Ingo Molnar wrote: >> >> > No, regular C code. >> > >> > I don't see the point of generating all this code via CPP - it's certainly not >> > making it more readable to me. I.e. this patch I commented on is a step backwards >> > for readability. >> >> Note that much of the atomic stuff we have today is all CPP already. > > Yeah, but there it's implementational: we pick up arch primitives depending on > whether they are defined, such as: > > #ifndef atomic_read_acquire > # define atomic_read_acquire(v) smp_load_acquire(&(v)->counter) > #endif > >> x86 is the exception because its 'weird', but most other archs are >> almost pure CPP -- check Alpha for example, or asm-generic/atomic.h. > > include/asm-generic/atomic.h looks pretty clean and readable overall. > >> Also, look at linux/atomic.h, its a giant maze of CPP. > > Nah, that's OK, much of is is essentially __weak inlines implemented via CPP - > i.e. CPP is filling in a missing compiler feature. > > But this patch I replied to appears to add instrumentation wrappery via CPP which > looks like excessive and avoidable obfuscation to me. > > If it's much more readable and much more compact than the C version then maybe, > but I'd like to see the C version first and see ... > >> The CPP help us generate functions, reduces endless copy/paste (which induces >> random differences -- read bugs) and construct variants depending on the >> architecture input. >> >> Yes, the CPP is a pain, but writing all that out explicitly is more of a >> pain. > > So I'm not convinced that it's true in this case. > > Could we see the C version and compare? I could be wrong about it all. Here it is (without instrumentation): https://gist.github.com/dvyukov/e33d580f701019e0cd99429054ff1f9a Instrumentation will add for each function: static __always_inline void atomic64_set(atomic64_t *v, long long i) { + kasan_check_write(v, sizeof(*v)); arch_atomic64_set(v, i); }