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Message-ID: <4ADD65C5.5000206@zytor.com> Date: Tue, 20 Oct 2009 16:24:53 +0900 From: "H. Peter Anvin" <hpa@...or.com> To: Eric Dumazet <eric.dumazet@...il.com> CC: Jan Beulich <JBeulich@...ell.com>, mingo@...e.hu, tglx@...utronix.de, linux-kernel@...r.kernel.org Subject: Re: [PATCH] x86-64: adjust ia32entry branches for better static prediction 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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