linux-kernel - Re: x86: use this_cpu for debug_stack

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Message-ID: <0000014054fd1db5-e6fbcc32-2e6c-49b1-83d4-399791ee6829-000000@email.amazonses.com>
Date:	Tue, 6 Aug 2013 18:56:49 +0000
From:	Christoph Lameter <cl@...two.org>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: x86: use this_cpu for debug_stack_usage

> Might as well change is_debug_stack() to use __this_cpu_read() instead
> of __get_cpu_var().





Subject: x86: use this_cpu for debug_stack_usage

Reduces overhead a bit and frees up a couple of registers.

Signed-off-by: Christoph Lameter <cl@...ux.com>

Index: linux/arch/x86/include/asm/debugreg.h
===================================================================
--- linux.orig/arch/x86/include/asm/debugreg.h	2013-08-06 13:52:23.740092873 -0500
+++ linux/arch/x86/include/asm/debugreg.h	2013-08-06 13:52:23.740092873 -0500
@@ -97,11 +97,11 @@ extern void hw_breakpoint_restore(void);
 DECLARE_PER_CPU(int, debug_stack_usage);
 static inline void debug_stack_usage_inc(void)
 {
-	__get_cpu_var(debug_stack_usage)++;
+	__this_cpu_inc(debug_stack_usage);
 }
 static inline void debug_stack_usage_dec(void)
 {
-	__get_cpu_var(debug_stack_usage)--;
+	__this_cpu_dec(debug_stack_usage);
 }
 int is_debug_stack(unsigned long addr);
 void debug_stack_set_zero(void);
Index: linux/arch/x86/kernel/cpu/common.c
===================================================================
--- linux.orig/arch/x86/kernel/cpu/common.c	2013-07-19 09:06:36.850047837 -0500
+++ linux/arch/x86/kernel/cpu/common.c	2013-08-06 13:54:36.426384889 -0500
@@ -1144,9 +1144,9 @@ DEFINE_PER_CPU(int, debug_stack_usage);

 int is_debug_stack(unsigned long addr)
 {
-	return __get_cpu_var(debug_stack_usage) ||
-		(addr <= __get_cpu_var(debug_stack_addr) &&
-		 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
+	return __this_cpu_read(debug_stack_usage) ||
+		(addr <= __this_cpu_read(debug_stack_addr) &&
+		 addr > (__this_cpu_read(debug_stack_addr) - DEBUG_STKSZ));
 }

 DEFINE_PER_CPU(u32, debug_idt_ctr);
--
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