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

[Eric Dumazet <dada1@cosmosbay.com>]

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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