From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754560AbYKQWJZ (ORCPT ); Mon, 17 Nov 2008 17:09:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752377AbYKQWJI (ORCPT ); Mon, 17 Nov 2008 17:09:08 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:47841 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752140AbYKQWJH (ORCPT ); Mon, 17 Nov 2008 17:09:07 -0500 Date: Mon, 17 Nov 2008 23:08:28 +0100 From: Ingo Molnar To: Linus Torvalds Cc: Eric Dumazet , David Miller , rjw@sisk.pl, linux-kernel@vger.kernel.org, kernel-testers@vger.kernel.org, cl@linux-foundation.org, efault@gmx.de, a.p.zijlstra@chello.nl, Stephen Hemminger Subject: Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28 Message-ID: <20081117220828.GB6398@elte.hu> References: <20081117110119.GL28786@elte.hu> <4921539B.2000002@cosmosbay.com> <20081117161135.GE12081@elte.hu> <49219D36.5020801@cosmosbay.com> <20081117170844.GJ12081@elte.hu> <20081117172549.GA27974@elte.hu> <4921AAD6.3010603@cosmosbay.com> <20081117182320.GA26844@elte.hu> <20081117184951.GA5585@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081117184951.GA5585@elte.hu> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00,DNS_FROM_SECURITYSAGE autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.0 DNS_FROM_SECURITYSAGE RBL: Envelope sender in blackholes.securitysage.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Ingo Molnar wrote: > 100.000000 total > ................ > 1.469183 tcp_current_mss hits (total: 146918) ......... ffffffff804c5237: 526 : ffffffff804c5237: 526 41 54 push %r12 ffffffff804c5239: 5929 55 push %rbp ffffffff804c523a: 32 53 push %rbx ffffffff804c523b: 294 48 89 fb mov %rdi,%rbx ffffffff804c523e: 539 48 83 ec 30 sub $0x30,%rsp ffffffff804c5242: 2590 85 f6 test %esi,%esi ffffffff804c5244: 444 48 8b 4f 78 mov 0x78(%rdi),%rcx ffffffff804c5248: 521 8b af 4c 04 00 00 mov 0x44c(%rdi),%ebp ffffffff804c524e: 791 74 2a je ffffffff804c527a ffffffff804c5250: 433 8b 87 00 01 00 00 mov 0x100(%rdi),%eax ffffffff804c5256: 236 c1 e0 10 shl $0x10,%eax ffffffff804c5259: 191 89 c2 mov %eax,%edx ffffffff804c525b: 487 23 97 fc 00 00 00 and 0xfc(%rdi),%edx ffffffff804c5261: 362 39 c2 cmp %eax,%edx ffffffff804c5263: 342 75 15 jne ffffffff804c527a ffffffff804c5265: 473 45 31 e4 xor %r12d,%r12d ffffffff804c5268: 221 8b 87 00 04 00 00 mov 0x400(%rdi),%eax ffffffff804c526e: 194 3b 87 80 04 00 00 cmp 0x480(%rdi),%eax ffffffff804c5274: 445 41 0f 94 c4 sete %r12b ffffffff804c5278: 261 eb 03 jmp ffffffff804c527d ffffffff804c527a: 0 45 31 e4 xor %r12d,%r12d ffffffff804c527d: 185 48 85 c9 test %rcx,%rcx ffffffff804c5280: 686 74 15 je ffffffff804c5297 ffffffff804c5282: 1806 8b 71 7c mov 0x7c(%rcx),%esi ffffffff804c5285: 1 3b b3 5c 03 00 00 cmp 0x35c(%rbx),%esi ffffffff804c528b: 21 74 0a je ffffffff804c5297 ffffffff804c528d: 0 48 89 df mov %rbx,%rdi ffffffff804c5290: 0 e8 8b fb ff ff callq ffffffff804c4e20 ffffffff804c5295: 0 89 c5 mov %eax,%ebp ffffffff804c5297: 864 48 8d 4c 24 28 lea 0x28(%rsp),%rcx ffffffff804c529c: 634 48 8d 54 24 10 lea 0x10(%rsp),%rdx ffffffff804c52a1: 995 31 f6 xor %esi,%esi ffffffff804c52a3: 0 48 89 df mov %rbx,%rdi ffffffff804c52a6: 2 e8 f2 fe ff ff callq ffffffff804c519d ffffffff804c52ab: 859 8b 8b e8 03 00 00 mov 0x3e8(%rbx),%ecx ffffffff804c52b1: 936 83 c0 14 add $0x14,%eax ffffffff804c52b4: 6 0f b7 d1 movzwl %cx,%edx ffffffff804c52b7: 0 39 d0 cmp %edx,%eax ffffffff804c52b9: 911 74 04 je ffffffff804c52bf ffffffff804c52bb: 0 29 d0 sub %edx,%eax ffffffff804c52bd: 0 29 c5 sub %eax,%ebp ffffffff804c52bf: 0 45 85 e4 test %r12d,%r12d ffffffff804c52c2: 6894 89 e8 mov %ebp,%eax ffffffff804c52c4: 0 74 38 je ffffffff804c52fe ffffffff804c52c6: 990 48 8b 83 68 03 00 00 mov 0x368(%rbx),%rax ffffffff804c52cd: 642 8b b3 04 01 00 00 mov 0x104(%rbx),%esi ffffffff804c52d3: 3 48 89 df mov %rbx,%rdi ffffffff804c52d6: 240 66 2b 70 30 sub 0x30(%rax),%si ffffffff804c52da: 588 66 2b b3 7e 03 00 00 sub 0x37e(%rbx),%si ffffffff804c52e1: 2 66 29 ce sub %cx,%si ffffffff804c52e4: 284 ff ce dec %esi ffffffff804c52e6: 664 0f b7 f6 movzwl %si,%esi ffffffff804c52e9: 2 e8 0a fb ff ff callq ffffffff804c4df8 ffffffff804c52ee: 68 0f b7 d0 movzwl %ax,%edx ffffffff804c52f1: 1870 89 c1 mov %eax,%ecx ffffffff804c52f3: 0 89 d0 mov %edx,%eax ffffffff804c52f5: 0 31 d2 xor %edx,%edx ffffffff804c52f7: 2135 f7 f5 div %ebp ffffffff804c52f9: 107010 89 c8 mov %ecx,%eax ffffffff804c52fb: 1670 66 29 d0 sub %dx,%ax ffffffff804c52fe: 0 66 89 83 ea 03 00 00 mov %ax,0x3ea(%rbx) ffffffff804c5305: 4 48 83 c4 30 add $0x30,%rsp ffffffff804c5309: 855 89 e8 mov %ebp,%eax ffffffff804c530b: 0 5b pop %rbx ffffffff804c530c: 797 5d pop %rbp ffffffff804c530d: 0 41 5c pop %r12 ffffffff804c530f: 0 c3 retq apparently this division causes 1.0% of tbench overhead: ffffffff804c52f5: 0 31 d2 xor %edx,%edx ffffffff804c52f7: 2135 f7 f5 div %ebp ffffffff804c52f9: 107010 89 c8 mov %ecx,%eax (gdb) list *0xffffffff804c52f7 0xffffffff804c52f7 is in tcp_current_mss (net/ipv4/tcp_output.c:1078). 1073 inet_csk(sk)->icsk_af_ops->net_header_len - 1074 inet_csk(sk)->icsk_ext_hdr_len - 1075 tp->tcp_header_len); 1076 1077 xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal); 1078 xmit_size_goal -= (xmit_size_goal % mss_now); 1079 } 1080 tp->xmit_size_goal = xmit_size_goal; 1081 1082 return mss_now; (gdb) it's this division: if (doing_tso) { [...] xmit_size_goal -= (xmit_size_goal % mss_now); Has no-one hit this before? Perhaps this is why switching loopback networking to TSO had a performance impact for others? It's still a bit weird ... how can a single division cause this much overhead? tcp_bound_to_half_wnd() [which is called straight before this sequence] seems low-overhead. Ingo