From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756014AbZJTHZ6 (ORCPT ); Tue, 20 Oct 2009 03:25:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755443AbZJTHZ5 (ORCPT ); Tue, 20 Oct 2009 03:25:57 -0400 Received: from terminus.zytor.com ([198.137.202.10]:57727 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755404AbZJTHZ5 (ORCPT ); Tue, 20 Oct 2009 03:25:57 -0400 Message-ID: <4ADD65C5.5000206@zytor.com> Date: Tue, 20 Oct 2009 16:24:53 +0900 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20091014 Fedora/3.0-2.8.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Eric Dumazet CC: Jan Beulich , mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86-64: adjust ia32entry branches for better static prediction References: <4ADD7E6C020000780001AD73@vpn.id2.novell.com> <4ADD64FC.3070006@gmail.com> In-Reply-To: <4ADD64FC.3070006@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/2009 04:21 PM, Eric Dumazet wrote: >> >> --- linux-2.6.32-rc5/arch/x86/ia32/ia32entry.S 2009-10-19 13:12:43.000000000 +0200 >> +++ 2.6.32-rc5-x86_64-ia32-syscall-trace-branch-dir/arch/x86/ia32/ia32entry.S 2009-10-19 09:36:39.000000000 +0200 >> @@ -249,9 +249,9 @@ sysenter_tracesys: >> call syscall_trace_enter >> LOAD_ARGS32 ARGOFFSET /* reload args from stack in case ptrace changed it */ >> RESTORE_REST >> - cmpl $(IA32_NR_syscalls-1),%eax >> - ja int_ret_from_sys_call /* sysenter_tracesys has set RAX(%rsp) */ >> - jmp sysenter_do_call >> + cmpl $IA32_NR_syscalls,%eax >> + jb sysenter_do_call >> + jmp int_ret_from_sys_call /* sysenter_tracesys has set RAX(%rsp) */ >> CFI_ENDPROC > > on cmov enabled build, we could use cmov instruction to load eax with number > that calls enosys_syscall(), to avoid loading -ENOSYS,RAX > and these branches... > It's x86-64, cmov is guaranteed. -hpa