From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933256AbaGWUBx (ORCPT ); Wed, 23 Jul 2014 16:01:53 -0400 Received: from mail-lb0-f173.google.com ([209.85.217.173]:39584 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932665AbaGWUBv (ORCPT ); Wed, 23 Jul 2014 16:01:51 -0400 MIME-Version: 1.0 In-Reply-To: <20140723191542.GA9398@linux.vnet.ibm.com> References: <1406092194-13004-1-git-send-email-bobby.prani@gmail.com> <1406092194-13004-10-git-send-email-bobby.prani@gmail.com> <20140723122112.GJ11241@linux.vnet.ibm.com> <20140723135024.GR11241@linux.vnet.ibm.com> <20140723142314.GV11241@linux.vnet.ibm.com> <20140723153018.GY11241@linux.vnet.ibm.com> <20140723191542.GA9398@linux.vnet.ibm.com> From: Pranith Kumar Date: Wed, 23 Jul 2014 16:01:19 -0400 Message-ID: Subject: Re: [PATCH 09/16] rcu: Remove redundant check for online cpu To: Paul McKenney Cc: Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , "open list:READ-COPY UPDATE..." 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 Wed, Jul 23, 2014 at 3:15 PM, Paul E. McKenney wrote: >> > If you change the "awake" to something like "am_online", I could get >> > behind this one. >> >> OK! I will submit that in the next series(with the zalloc check). > > You caught me at a weak moment... This change just adds an extra > line of code and doesn't really help anything. > > So please leave this one out. > It adds an extra line of code and generates better assembly code. Last try to convince you before I give up :-) Before: if (!rcu_is_watching() && cpu_online(smp_processor_id())) 26d3: 83 e2 01 and $0x1,%edx 26d6: 75 1f jne 26f7 <__call_rcu+0x1c7> 26d8: 65 8b 14 25 00 00 00 mov %gs:0x0,%edx 26df: 00 26dc: R_X86_64_32S cpu_number 26e0: 48 8b 0d 00 00 00 00 mov 0x0(%rip),%rcx # 26e7 <__call_rcu+0x1b7> 26e3: R_X86_64_PC32 cpu_online_mask-0x4 26e7: 89 d2 mov %edx,%edx 26e9: 48 0f a3 11 bt %rdx,(%rcx) 26ed: 19 d2 sbb %edx,%edx 26ef: 85 d2 test %edx,%edx 26f1: 0f 85 29 02 00 00 jne 2920 <__call_rcu+0x3f0> invoke_rcu_core(); /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) 26f7: 48 f7 45 d0 00 02 00 testq $0x200,-0x30(%rbp) 26fe: 00 26ff: 0f 84 e6 fe ff ff je 25eb <__call_rcu+0xbb> 2705: 65 8b 14 25 00 00 00 mov %gs:0x0,%edx 270c: 00 2709: R_X86_64_32S cpu_number 270d: 48 8b 0d 00 00 00 00 mov 0x0(%rip),%rcx # 2714 <__call_rcu+0x1e4> 2710: R_X86_64_PC32 cpu_online_mask-0x4 2714: 89 d2 mov %edx,%edx 2716: 48 0f a3 11 bt %rdx,(%rcx) 271a: 19 d2 sbb %edx,%edx 271c: 85 d2 test %edx,%edx 271e: 0f 84 c7 fe ff ff je 25eb <__call_rcu+0xbb> After: bool cpu_up = cpu_online(smp_processor_id()); 26c1: 65 8b 14 25 00 00 00 mov %gs:0x0,%edx 26c8: 00 26c5: R_X86_64_32S cpu_number 26c9: 48 8b 0d 00 00 00 00 mov 0x0(%rip),%rcx # 26d0 <__call_rcu+0x1a0> 26cc: R_X86_64_PC32 cpu_online_mask-0x4 26d0: 89 d2 mov %edx,%edx 26d2: 48 0f a3 11 bt %rdx,(%rcx) 26d6: 19 d2 sbb %edx,%edx 26d8: 85 d2 test %edx,%edx 26da: 41 0f 95 c4 setne %r12b if (!rcu_is_watching() && cpu_up) 26f0: 83 e2 01 and $0x1,%edx 26f3: 75 09 jne 26fe <__call_rcu+0x1ce> 26f5: 45 84 e4 test %r12b,%r12b 26f8: 0f 85 12 02 00 00 jne 2910 <__call_rcu+0x3e0> invoke_rcu_core(); /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ if (irqs_disabled_flags(flags) || !cpu_up) 26fe: 48 f7 45 d0 00 02 00 testq $0x200,-0x30(%rbp) 2705: 00 2706: 0f 84 df fe ff ff je 25eb <__call_rcu+0xbb> 270c: 45 84 e4 test %r12b,%r12b 270f: 0f 84 d6 fe ff ff je 25eb <__call_rcu+0xbb> -- Pranith