* [PATCH] cmpxchg: Discard unnecessary cast to volatile
@ 2014-10-01 17:57 Pranith Kumar
2014-10-20 20:22 ` Pranith Kumar
0 siblings, 1 reply; 5+ messages in thread
From: Pranith Kumar @ 2014-10-01 17:57 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
maintainer:X86 ARCHITECTURE..., Borislav Petkov,
open list:X86 ARCHITECTURE...
Generating a volatile pointer is really not necessary here. This is the only
location where a volatile pointer is being generated for use in asm.
This commit removes the unnecessary volatile pointer being created.
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
arch/x86/include/asm/cmpxchg.h | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index 99c105d7..f0baea8 100644
--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -90,36 +90,32 @@ extern void __add_wrong_size(void)
switch (size) { \
case __X86_CASE_B: \
{ \
- volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile(lock "cmpxchgb %2,%1" \
- : "=a" (__ret), "+m" (*__ptr) \
+ : "=a" (__ret), "+m" (*ptr) \
: "q" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case __X86_CASE_W: \
{ \
- volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile(lock "cmpxchgw %2,%1" \
- : "=a" (__ret), "+m" (*__ptr) \
+ : "=a" (__ret), "+m" (*ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case __X86_CASE_L: \
{ \
- volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile(lock "cmpxchgl %2,%1" \
- : "=a" (__ret), "+m" (*__ptr) \
+ : "=a" (__ret), "+m" (*ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
} \
case __X86_CASE_Q: \
{ \
- volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile(lock "cmpxchgq %2,%1" \
- : "=a" (__ret), "+m" (*__ptr) \
+ : "=a" (__ret), "+m" (*ptr) \
: "r" (__new), "0" (__old) \
: "memory"); \
break; \
--
1.9.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile
2014-10-01 17:57 [PATCH] cmpxchg: Discard unnecessary cast to volatile Pranith Kumar
@ 2014-10-20 20:22 ` Pranith Kumar
2014-10-21 10:14 ` Peter Zijlstra
0 siblings, 1 reply; 5+ messages in thread
From: Pranith Kumar @ 2014-10-20 20:22 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
maintainer:X86 ARCHITECTURE..., Borislav Petkov,
open list:X86 ARCHITECTURE..., Peter Zijlstra
ping.
On Wed, Oct 1, 2014 at 1:57 PM, Pranith Kumar <bobby.prani@gmail.com> wrote:
> Generating a volatile pointer is really not necessary here. This is the only
> location where a volatile pointer is being generated for use in asm.
>
> This commit removes the unnecessary volatile pointer being created.
>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> ---
> arch/x86/include/asm/cmpxchg.h | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
> index 99c105d7..f0baea8 100644
> --- a/arch/x86/include/asm/cmpxchg.h
> +++ b/arch/x86/include/asm/cmpxchg.h
> @@ -90,36 +90,32 @@ extern void __add_wrong_size(void)
> switch (size) { \
> case __X86_CASE_B: \
> { \
> - volatile u8 *__ptr = (volatile u8 *)(ptr); \
> asm volatile(lock "cmpxchgb %2,%1" \
> - : "=a" (__ret), "+m" (*__ptr) \
> + : "=a" (__ret), "+m" (*ptr) \
> : "q" (__new), "0" (__old) \
> : "memory"); \
> break; \
> } \
> case __X86_CASE_W: \
> { \
> - volatile u16 *__ptr = (volatile u16 *)(ptr); \
> asm volatile(lock "cmpxchgw %2,%1" \
> - : "=a" (__ret), "+m" (*__ptr) \
> + : "=a" (__ret), "+m" (*ptr) \
> : "r" (__new), "0" (__old) \
> : "memory"); \
> break; \
> } \
> case __X86_CASE_L: \
> { \
> - volatile u32 *__ptr = (volatile u32 *)(ptr); \
> asm volatile(lock "cmpxchgl %2,%1" \
> - : "=a" (__ret), "+m" (*__ptr) \
> + : "=a" (__ret), "+m" (*ptr) \
> : "r" (__new), "0" (__old) \
> : "memory"); \
> break; \
> } \
> case __X86_CASE_Q: \
> { \
> - volatile u64 *__ptr = (volatile u64 *)(ptr); \
> asm volatile(lock "cmpxchgq %2,%1" \
> - : "=a" (__ret), "+m" (*__ptr) \
> + : "=a" (__ret), "+m" (*ptr) \
> : "r" (__new), "0" (__old) \
> : "memory"); \
> break; \
> --
> 1.9.1
>
--
Pranith
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile
2014-10-20 20:22 ` Pranith Kumar
@ 2014-10-21 10:14 ` Peter Zijlstra
2014-10-21 15:48 ` H. Peter Anvin
0 siblings, 1 reply; 5+ messages in thread
From: Peter Zijlstra @ 2014-10-21 10:14 UTC (permalink / raw)
To: Pranith Kumar
Cc: Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
maintainer:X86 ARCHITECTURE..., Borislav Petkov,
open list:X86 ARCHITECTURE...
On Mon, Oct 20, 2014 at 04:22:27PM -0400, Pranith Kumar wrote:
> > Generating a volatile pointer is really not necessary here. This is the only
> > location where a volatile pointer is being generated for use in asm.
> >
> > This commit removes the unnecessary volatile pointer being created.
> >
> > Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Seems sane enough to me.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile
2014-10-21 10:14 ` Peter Zijlstra
@ 2014-10-21 15:48 ` H. Peter Anvin
2014-10-21 22:15 ` Pranith Kumar
0 siblings, 1 reply; 5+ messages in thread
From: H. Peter Anvin @ 2014-10-21 15:48 UTC (permalink / raw)
To: Peter Zijlstra, Pranith Kumar
Cc: Thomas Gleixner, Ingo Molnar, maintainer:X86 ARCHITECTURE...,
Borislav Petkov, open list:X86 ARCHITECTURE...
On 10/21/2014 03:14 AM, Peter Zijlstra wrote:
> On Mon, Oct 20, 2014 at 04:22:27PM -0400, Pranith Kumar wrote:
>>> Generating a volatile pointer is really not necessary here. This is the only
>>> location where a volatile pointer is being generated for use in asm.
>>>
>>> This commit removes the unnecessary volatile pointer being created.
>>>
>>> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
>
> Seems sane enough to me.
>
However, it seems like unnecessary churn. Does the volatile hurt in any
way?
-hpa
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile
2014-10-21 15:48 ` H. Peter Anvin
@ 2014-10-21 22:15 ` Pranith Kumar
0 siblings, 0 replies; 5+ messages in thread
From: Pranith Kumar @ 2014-10-21 22:15 UTC (permalink / raw)
To: H. Peter Anvin
Cc: Peter Zijlstra, Thomas Gleixner, Ingo Molnar,
maintainer:X86 ARCHITECTURE..., Borislav Petkov,
open list:X86 ARCHITECTURE...
On Tue, Oct 21, 2014 at 11:48 AM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 10/21/2014 03:14 AM, Peter Zijlstra wrote:
>> On Mon, Oct 20, 2014 at 04:22:27PM -0400, Pranith Kumar wrote:
>>>> Generating a volatile pointer is really not necessary here. This is the only
>>>> location where a volatile pointer is being generated for use in asm.
>>>>
>>>> This commit removes the unnecessary volatile pointer being created.
>>>>
>>>> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
>>
>> Seems sane enough to me.
>>
>
> However, it seems like unnecessary churn. Does the volatile hurt in any
> way?
Removing 4 lines of unnecessary code seems to be worthwhile to me.
Also, we reduce the unnecessary use of 'volatile' data types which
IMHO makes this a good little clean up.
I am not sure if the use of volatile actually causes any loss of
chances of optimization. I've tried to come up with cases where this
happens and was unsuccessful.
--
Pranith
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2014-10-21 22:16 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2014-10-01 17:57 [PATCH] cmpxchg: Discard unnecessary cast to volatile Pranith Kumar
2014-10-20 20:22 ` Pranith Kumar
2014-10-21 10:14 ` Peter Zijlstra
2014-10-21 15:48 ` H. Peter Anvin
2014-10-21 22:15 ` Pranith Kumar
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