[PATCH] x86_64 prefetchw() function can take into account CONFIG_MK8 / CONFIG_MPSC

[PATCH] x86_64 prefetchw() function can take into account CONFIG_MK8 / CONFIG_MPSC

[Eric Dumazet]

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If we build a x86_64 kernel for an AMD64 or for an Intel EMT64, no need to use alternative_input.
Reserve alternative_input only for a generic kernel.





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diff -Nru linux-2.6.12/include/asm-x86_64/processor.h linux-2.6.12-orig/include/asm-x86_64/processor.h
--- linux-2.6.12-orig/include/asm-x86_64/processor.h 2005-06-17 21:48:29.000000000 +0200
+++ linux-2.6.12/include/asm-x86_64/processor.h       2005-06-23 11:20:08.000000000 +0200
@@ -389,10 +389,21 @@
 #define ARCH_HAS_PREFETCHW 1
 static inline void prefetchw(void *x)
 {
+#if defined(CONFIG_MK8)
+       /* AMD64 / MK8 has 3DNOW, we can emit a true prefetchw, using a "m" in the asm input */
+       asm volatile("prefetchw %0" :: "m" (*(unsigned long *)x));
+#elif defined(CONFIG_MPSC)
+       /* Intel EMT64 does not have 3DNOW, no prefetchw instruction */
+#else
+       /* If we build a generic X86_64 kernel,
+        * we must use alternative_input() and a "r" asm constraint to make sure
+        * the size of the instruction will be <= 5
+        */
        alternative_input(ASM_NOP5,
                          "prefetchw (%1)",
                          X86_FEATURE_3DNOW,
                          "r" (x));
+#endif
 }

 #define ARCH_HAS_SPINLOCK_PREFETCH 1

[PATCH] x86_64 prefetchw() function can take into account CONFIG_MK8 / CONFIG_MPSC

[Eric Dumazet]

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If we build a x86_64 kernel for an AMD64 or for an Intel EMT64, no need to use alternative_input.
Reserve alternative_input only for a generic kernel.

Thank you

Eric Dumazet

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>


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diff -Nru linux-2.6.12/include/asm-x86_64/processor.h linux-2.6.12-orig/include/asm-x86_64/processor.h
--- linux-2.6.12-orig/include/asm-x86_64/processor.h 2005-06-17 21:48:29.000000000 +0200
+++ linux-2.6.12/include/asm-x86_64/processor.h       2005-06-23 11:20:08.000000000 +0200
@@ -389,10 +389,21 @@
 #define ARCH_HAS_PREFETCHW 1
 static inline void prefetchw(void *x)
 {
+#if defined(CONFIG_MK8)
+       /* AMD64 / MK8 has 3DNOW, we can emit a true prefetchw, using a "m" in the asm input */
+       asm volatile("prefetchw %0" :: "m" (*(unsigned long *)x));
+#elif defined(CONFIG_MPSC)
+       /* Intel EMT64 does not have 3DNOW, no prefetchw instruction */
+#else
+       /* If we build a generic X86_64 kernel,
+        * we must use alternative_input() and a "r" asm constraint to make sure
+        * the size of the instruction will be <= 5
+        */
        alternative_input(ASM_NOP5,
                          "prefetchw (%1)",
                          X86_FEATURE_3DNOW,
                          "r" (x));
+#endif
 }

 #define ARCH_HAS_SPINLOCK_PREFETCH 1

Re: [PATCH] x86_64 prefetchw() function can take into account CONFIG_MK8 / CONFIG_MPSC

[Andi Kleen]

On Thu, Jun 23, 2005 at 11:32:34AM +0200, Eric Dumazet wrote:
> If we build a x86_64 kernel for an AMD64 or for an Intel EMT64, no need to 
> use alternative_input.
> Reserve alternative_input only for a generic kernel.

An EM64T kernel should still boot on AMD64 and vice versa. Rejected.

-Andi

Re: [PATCH] x86_64 prefetchw() function can take into account CONFIG_MK8 / CONFIG_MPSC

[Eric Dumazet]

Andi Kleen a écrit :
> On Thu, Jun 23, 2005 at 11:32:34AM +0200, Eric Dumazet wrote:
> 
>>If we build a x86_64 kernel for an AMD64 or for an Intel EMT64, no need to 
>>use alternative_input.
>>Reserve alternative_input only for a generic kernel.
> 
> 
> An EM64T kernel should still boot on AMD64 and vice versa. Rejected.
> 
> -Andi
> 
> 

OK, I wrongly assumed the 'MK8' or 'MPSC' choices were like x86 choices :

A kernel compiled for a Pentium-4 will not run on a i486.

But then what is the meaning of the choice "Generic-x86-64" in the "Processor family" menu ?
The Help message is : CONFIG_GENERIC_CPU: Generic x86-64 CPU.

Eric

Re: [PATCH] x86_64 prefetchw() function can take into account CONFIG_MK8 / CONFIG_MPSC

[Andi Kleen]

On Thu, Jun 23, 2005 at 02:53:14PM +0200, Eric Dumazet wrote:
> Andi Kleen a ?crit :
> >On Thu, Jun 23, 2005 at 11:32:34AM +0200, Eric Dumazet wrote:
> >
> >>If we build a x86_64 kernel for an AMD64 or for an Intel EMT64, no need 
> >>to use alternative_input.
> >>Reserve alternative_input only for a generic kernel.
> >
> >
> >An EM64T kernel should still boot on AMD64 and vice versa. Rejected.
> >
> >-Andi
> >
> >
> 
> OK, I wrongly assumed the 'MK8' or 'MPSC' choices were like x86 choices :
> 
> A kernel compiled for a Pentium-4 will not run on a i486.
> 
> But then what is the meaning of the choice "Generic-x86-64" in the 
> "Processor family" menu ?
> The Help message is : CONFIG_GENERIC_CPU: Generic x86-64 CPU.

Optimize for both. It's a catch all setting for future changes
and does not do too much right now.

It also won't pass any -mcpu=... arguments to gcc. This currently
doesn't make any difference (gcc x86-64 default is to optimize
for K8), but I assume it might at some point when gcc gets
a "combined" mode that optimizes for both Intel and AMD CPUs.

-Andi