From: Benjamin LaHaise <bcrl@kvack.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Alexander van Heukelum <heukelum@mailshack.com>
Subject: [PATCH] x86-64: remove locked instruction from switch_to()
Date: Sat, 10 Jan 2009 23:00:22 -0500 [thread overview]
Message-ID: <20090111040022.GG13467@kvack.org> (raw)
In-Reply-To: <20090110223616.GB16719@elte.hu>
Here is a rediffed and test booted version of the patch against linus' git
tree as of a couple of hours ago.
The patch below removes an unnecessary locked instruction from
switch_to(). TIF_FORK is only ever set in copy_thread() on initial
process creation, and gets cleared during the first scheduling of the
process. As such, it is safe to use an unlocked test for the flag
within switch_to()./
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index 8e626ea..fa47b1e 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -96,15 +96,15 @@ do { \
"thread_return:\n\t" \
"movq %%gs:%P[pda_pcurrent],%%rsi\n\t" \
"movq %P[thread_info](%%rsi),%%r8\n\t" \
- LOCK_PREFIX "btr %[tif_fork],%P[ti_flags](%%r8)\n\t" \
"movq %%rax,%%rdi\n\t" \
- "jc ret_from_fork\n\t" \
+ "testl %[_tif_fork],%P[ti_flags](%%r8)\n\t" \
+ "jnz ret_from_fork\n\t" \
RESTORE_CONTEXT \
: "=a" (last) \
: [next] "S" (next), [prev] "D" (prev), \
[threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
[ti_flags] "i" (offsetof(struct thread_info, flags)), \
- [tif_fork] "i" (TIF_FORK), \
+ [_tif_fork] "i" (_TIF_FORK), \
[thread_info] "i" (offsetof(struct task_struct, stack)), \
[pda_pcurrent] "i" (offsetof(struct x8664_pda, pcurrent)) \
: "memory", "cc" __EXTRA_CLOBBER)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e28c7a9..38dd374 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -408,6 +408,8 @@ END(save_paranoid)
ENTRY(ret_from_fork)
DEFAULT_FRAME
+ LOCK ; btr $TIF_FORK,TI_flags(%r8)
+
push kernel_eflags(%rip)
CFI_ADJUST_CFA_OFFSET 8
popf # reset kernel eflags
next prev parent reply other threads:[~2009-01-11 4:00 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-10 21:26 [x86-64] remove locked instruction from switch_to() Benjamin LaHaise
2009-01-10 22:36 ` Ingo Molnar
2009-01-11 4:00 ` Benjamin LaHaise [this message]
2009-01-11 4:05 ` [PATCH] x86-64: " Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20090111040022.GG13467@kvack.org \
--to=bcrl@kvack.org \
--cc=heukelum@mailshack.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.