lkml.org 
[lkml]   [2010]   [Sep]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] x86, percpu: Fix __this_cpu_ptr with const pointers
I folded the fix into the original patch and also updated the address
space casting for sparse.

Thanks.

From 9c5b46f782cde2c88a5e4f02a6112bfcfb105f8f Mon Sep 17 00:00:00 2001
From: Brian Gerst <brgerst@gmail.com>
Date: Thu, 9 Sep 2010 18:17:26 +0200
Subject: [PATCH] x86, percpu: Optimize this_cpu_ptr

Allow arches to implement __this_cpu_ptr, and provide an x86 version.

Before:
movq $foo, %rax
movq %gs:this_cpu_off, %rdx
addq %rdx, %rax

After:
movq $foo, %rax
addq %gs:this_cpu_off, %rax

The benefit is doing it in one less instruction and not clobbering
a temporary register.

tj: * Beefed up the comment a bit and renamed in-macro temp variable
to match neighboring macros.

* Folded fix for const pointer case found in linux-next.

* Fixed sparse notation.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
arch/x86/include/asm/percpu.h | 14 ++++++++++++++
include/asm-generic/percpu.h | 9 +++++++--
2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index cd28f9a..f899e01 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -47,6 +47,20 @@
#ifdef CONFIG_SMP
#define __percpu_arg(x) "%%"__stringify(__percpu_seg)":%P" #x
#define __my_cpu_offset percpu_read(this_cpu_off)
+
+/*
+ * Compared to the generic __my_cpu_offset version, the following
+ * saves one instruction and avoids clobbering a temp register.
+ */
+#define __this_cpu_ptr(ptr) \
+({ \
+ unsigned long tcp_ptr__; \
+ __verify_pcpu_ptr(ptr); \
+ asm volatile("add " __percpu_arg(1) ", %0" \
+ : "=r" (tcp_ptr__) \
+ : "m" (this_cpu_off), "0" (ptr)); \
+ (typeof(*(ptr)) __kernel __force *)tcp_ptr__; \
+})
#else
#define __percpu_arg(x) "%P" #x
#endif
diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index 08923b6..ec64311 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -60,9 +60,14 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
#define __raw_get_cpu_var(var) \
(*SHIFT_PERCPU_PTR(&(var), __my_cpu_offset))

-#define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset)
+#ifndef __this_cpu_ptr
#define __this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
-
+#endif
+#ifdef CONFIG_DEBUG_PREEMPT
+#define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset)
+#else
+#define this_cpu_ptr(ptr) __this_cpu_ptr(ptr)
+#endif

#ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
extern void setup_per_cpu_areas(void);
--
1.7.1


\
 
 \ /
  Last update: 2010-09-10 10:37    [W:0.032 / U:1.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site