From: Joerg Roedel <[email protected]>
This patch modifies the get_cycles_sync() function on i386 and x86_64 to
use the RDTSCP (if it is available) instruction to synchronize with the
CPU core and not CPUID. This is especially usefull when running Linux as
a KVM guest because CPUID is intercepted and will cause a VMEXIT there.
Signed-off-by: Joerg Roedel <[email protected]>
--
Joerg Roedel
Operating System Research Center
AMD Saxony LLC & Co. KG
diff --git a/include/asm-i386/cpufeature.h b/include/asm-i386/cpufeature.h
index 3f92b94..7275e41 100644
--- a/include/asm-i386/cpufeature.h
+++ b/include/asm-i386/cpufeature.h
@@ -49,6 +49,7 @@
#define X86_FEATURE_MP (1*32+19) /* MP Capable. */
#define X86_FEATURE_NX (1*32+20) /* Execute Disable */
#define X86_FEATURE_MMXEXT (1*32+22) /* AMD MMX extensions */
+#define X86_FEATURE_RDTSCP (1*32+27) /* RDTSCP */
#define X86_FEATURE_LM (1*32+29) /* Long Mode (x86-64) */
#define X86_FEATURE_3DNOWEXT (1*32+30) /* AMD 3DNow! extensions */
#define X86_FEATURE_3DNOW (1*32+31) /* 3DNow! */
diff --git a/include/asm-x86_64/tsc.h b/include/asm-x86_64/tsc.h
index 9a0a368..7db952d 100644
--- a/include/asm-x86_64/tsc.h
+++ b/include/asm-x86_64/tsc.h
@@ -34,22 +34,28 @@ static inline cycles_t get_cycles(void)
/* Like get_cycles, but make sure the CPU is synchronized. */
static __always_inline cycles_t get_cycles_sync(void)
{
- unsigned long long ret;
-#ifdef X86_FEATURE_SYNC_RDTSC
+ unsigned int a, d;
unsigned eax;
+#ifdef X86_FEATURE_SYNC_RDTSC
/*
* Don't do an additional sync on CPUs where we know
* RDTSC is already synchronous:
*/
alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
"=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
+ /* We use RDTSCP if it is available, no extra CPUID required then */
+ alternative_add_one(ASM_NOP2, X86_FEATURE_RDTSCP);
#else
- sync_core();
+ /* no CPUID required if we use RDTSCP */
+ alternative_io("cpuid", ASM_NOP2, X86_FEATURE_RDTSCP,
+ "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
#endif
- rdtscll(ret);
- return ret;
+ alternative_io("rdtsc\n" ASM_NOP1, "rdtscp", X86_FEATURE_RDTSCP,
+ ALTERNATIVE_OUTPUT2("=a" (a), "=d" (d)), "0" (1) : "ecx","memory");
+
+ return ((unsigned long long)a) | ((unsigned long long)d) << 32;
}
extern void tsc_init(void);
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