linux-kernel - Re: [cpuops cmpxchg double V1 2/4] x86: this_cpu_cmpxchg

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Message-ID: <alpine.DEB.2.00.1012151149560.14964@router.home>
Date:	Wed, 15 Dec 2010 11:53:31 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Tejun Heo <tj@...nel.org>, akpm@...ux-foundation.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg double V1 2/4] x86: this_cpu_cmpxchg_double()
 support

On Wed, 15 Dec 2010, H. Peter Anvin wrote:

> >  cmpxchg16b_cpuops_emu:
> >  	pushf
> >  	cli
> >
>
> Could we rename it this_cpu_cmpxchg16b_emu or something like that?

Ok. New fixup patch:



Subject: x86, percpu: Rename cmpxchg16b_cpuops_emu to this_cpu_cmpxchg16b_emu

Rename the function to make clear what it is used for. Also add some comments
to explain the nature of the atomicness.

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

---
 arch/x86/include/asm/percpu.h |    2 +-
 arch/x86/lib/cmpxchg16b_emu.S |   10 +++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

Index: linux-2.6/arch/x86/lib/cmpxchg16b_emu.S
===================================================================
--- linux-2.6.orig/arch/x86/lib/cmpxchg16b_emu.S	2010-12-15 10:57:21.000000000 -0600
+++ linux-2.6/arch/x86/lib/cmpxchg16b_emu.S	2010-12-15 11:47:50.000000000 -0600
@@ -23,14 +23,18 @@
  * %rcx : high 64 bits of new value
  * %al  : Operation successful
  */
-ENTRY(cmpxchg16b_cpuops_emu)
+ENTRY(this_cpu_cmpxchg16b_emu)
 CFI_STARTPROC

 #
 # Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in
 # al not via the ZF. Caller will access al to get result.
 #
-cmpxchg16b_cpuops_emu:
+# Note that this is only useful for a cpuops operation. Meaning that we
+# do *not* have a fully atomic operation but just an operation that is
+# *atomic* on a single cpu (as provided by the this_cpu_xx class of macros)
+#
+this_cpu_cmpxchg16b_emu:
 	pushf
 	cli

@@ -53,6 +57,6 @@ cmpxchg16b_cpuops_emu:

 CFI_ENDPROC

-ENDPROC(cmpxchg16b_cpuops)
+ENDPROC(this_cpu_cmpxchg16b_emu)


Index: linux-2.6/arch/x86/include/asm/percpu.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/percpu.h	2010-12-15 11:48:09.000000000 -0600
+++ linux-2.6/arch/x86/include/asm/percpu.h	2010-12-15 11:48:26.000000000 -0600
@@ -520,7 +520,7 @@ do {									\
 	typeof(o2) __o2 = o2;						\
 	typeof(o2) __n2 = n2;						\
 	typeof(o2) __dummy;						\
-	alternative_io("call cmpxchg16b_cpuops_emu\n\t" P6_NOP4,		\
+	alternative_io("call this_cpu_cmpxchg16b_emu\n\t" P6_NOP4,		\
 			"cmpxchg16b %%gs:(%%rsi)\n\tsetz %0\n\t",	\
 			X86_FEATURE_CX16,				\
 		    	ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)),	\
--
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