Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755542Ab3F1LT4 (ORCPT ); Fri, 28 Jun 2013 07:19:56 -0400 Received: from mail-ee0-f47.google.com ([74.125.83.47]:34476 "EHLO mail-ee0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755234Ab3F1LTz (ORCPT ); Fri, 28 Jun 2013 07:19:55 -0400 Date: Fri, 28 Jun 2013 13:19:48 +0200 From: Ingo Molnar To: Wedson Almeida Filho Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton , Peter Zijlstra Subject: Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64 Message-ID: <20130628111948.GA31065@gmail.com> References: <1372416851-56830-1-git-send-email-wedsonaf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1372416851-56830-1-git-send-email-wedsonaf@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4793 Lines: 95 * Wedson Almeida Filho wrote: > The new implementation allows the compiler to better optimize the code; the > original implementation is still used when the kernel is compiled with older > versions of gcc that don't support asm-goto. > > Compiling with gcc 4.7.3, the original mutex_lock() is 60 bytes with the fast > path taking 16 instructions; the new mutex_lock() is 42 bytes, with the fast > path taking 12 instructions. > > The original mutex_unlock() is 24 bytes with the fast path taking 7 > instructions; the new mutex_unlock() is 25 bytes (because the compiler used > a 2-byte ret) with the fast path taking 4 instructions. > > The two versions of the functions are included below for reference. > > Old: > ffffffff817742a0 : > ffffffff817742a0: 55 push %rbp > ffffffff817742a1: 48 89 e5 mov %rsp,%rbp > ffffffff817742a4: 48 83 ec 10 sub $0x10,%rsp > ffffffff817742a8: 48 89 5d f0 mov %rbx,-0x10(%rbp) > ffffffff817742ac: 48 89 fb mov %rdi,%rbx > ffffffff817742af: 4c 89 65 f8 mov %r12,-0x8(%rbp) > ffffffff817742b3: e8 28 15 00 00 callq ffffffff817757e0 <_cond_resched> > ffffffff817742b8: 48 89 df mov %rbx,%rdi > ffffffff817742bb: f0 ff 0f lock decl (%rdi) > ffffffff817742be: 79 05 jns ffffffff817742c5 > ffffffff817742c0: e8 cb 04 00 00 callq ffffffff81774790 <__mutex_lock_slowpath> > ffffffff817742c5: 65 48 8b 04 25 c0 b7 mov %gs:0xb7c0,%rax > ffffffff817742cc: 00 00 > ffffffff817742ce: 4c 8b 65 f8 mov -0x8(%rbp),%r12 > ffffffff817742d2: 48 89 43 18 mov %rax,0x18(%rbx) > ffffffff817742d6: 48 8b 5d f0 mov -0x10(%rbp),%rbx > ffffffff817742da: c9 leaveq > ffffffff817742db: c3 retq > > ffffffff81774250 : > ffffffff81774250: 55 push %rbp > ffffffff81774251: 48 c7 47 18 00 00 00 movq $0x0,0x18(%rdi) > ffffffff81774258: 00 > ffffffff81774259: 48 89 e5 mov %rsp,%rbp > ffffffff8177425c: f0 ff 07 lock incl (%rdi) > ffffffff8177425f: 7f 05 jg ffffffff81774266 > ffffffff81774261: e8 ea 04 00 00 callq ffffffff81774750 <__mutex_unlock_slowpath> > ffffffff81774266: 5d pop %rbp > ffffffff81774267: c3 retq > > New: > ffffffff81774920 : > ffffffff81774920: 55 push %rbp > ffffffff81774921: 48 89 e5 mov %rsp,%rbp > ffffffff81774924: 53 push %rbx > ffffffff81774925: 48 89 fb mov %rdi,%rbx > ffffffff81774928: e8 a3 0e 00 00 callq ffffffff817757d0 <_cond_resched> > ffffffff8177492d: f0 ff 0b lock decl (%rbx) > ffffffff81774930: 79 08 jns ffffffff8177493a > ffffffff81774932: 48 89 df mov %rbx,%rdi > ffffffff81774935: e8 16 fe ff ff callq ffffffff81774750 <__mutex_lock_slowpath> > ffffffff8177493a: 65 48 8b 04 25 c0 b7 mov %gs:0xb7c0,%rax > ffffffff81774941: 00 00 > ffffffff81774943: 48 89 43 18 mov %rax,0x18(%rbx) > ffffffff81774947: 5b pop %rbx > ffffffff81774948: 5d pop %rbp > ffffffff81774949: c3 retq > > ffffffff81774730 : > ffffffff81774730: 48 c7 47 18 00 00 00 movq $0x0,0x18(%rdi) > ffffffff81774737: 00 > ffffffff81774738: f0 ff 07 lock incl (%rdi) > ffffffff8177473b: 7f 0a jg ffffffff81774747 > ffffffff8177473d: 55 push %rbp > ffffffff8177473e: 48 89 e5 mov %rsp,%rbp > ffffffff81774741: e8 aa ff ff ff callq ffffffff817746f0 <__mutex_unlock_slowpath> > ffffffff81774746: 5d pop %rbp > ffffffff81774747: f3 c3 repz retq Very nice! One detail: > +#if defined(CC_HAVE_ASM_GOTO) > +#if defined(CC_HAVE_ASM_GOTO) Please change these to #ifdef. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/