From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jan Beulich <JBeulich@novell.com>
Cc: mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86-64: adjust ia32entry branches for better static prediction
Date: Tue, 20 Oct 2009 09:21:32 +0200 [thread overview]
Message-ID: <4ADD64FC.3070006@gmail.com> (raw)
In-Reply-To: <4ADD7E6C020000780001AD73@vpn.id2.novell.com>
Jan Beulich a écrit :
> Swap branch pairs so that the static branch prediction logic would
> consider the syscall-number-in-range case the taken path.
>
> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>
> ---
> arch/x86/ia32/ia32entry.S | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> --- 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...
next prev parent reply other threads:[~2009-10-20 7:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-20 7:10 [PATCH] x86-64: adjust ia32entry branches for better static prediction Jan Beulich
2009-10-20 7:21 ` Eric Dumazet [this message]
2009-10-20 7:24 ` H. Peter Anvin
2009-10-26 8:28 ` Andi Kleen
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