Hi, Andi:
The attached patch (actually, git show output) makes my Dell 1501 to hang
on boot. Sorry, I have no clue why... The culprit is found with git bisect.
But yes, it's an AMD MK-36. I use an x86_64 kernel. It is 100% reproducible.
Cheers,
-- Pete
commit c5bcb5635a03da3158f121ae20ccbbf72b4fc62a
Author: Andi Kleen <[email protected]>
Date: Wed May 2 19:27:21 2007 +0200
[PATCH] x86: Use RDTSCP for synchronous get_cycles if possible
RDTSCP is already synchronous and doesn't need an explicit CPUID.
This is a little faster and more importantly avoids VMEXITs on Hypervisors.
Original patch from Joerg Roedel, but reworked by AK
Also includes miscompilation fix by Eric Biederman
Cc: "Joerg Roedel" <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
diff --git a/include/asm-i386/tsc.h b/include/asm-i386/tsc.h
index 0181f9d..3f3c1fa 100644
--- a/include/asm-i386/tsc.h
+++ b/include/asm-i386/tsc.h
@@ -38,6 +38,15 @@ static __always_inline cycles_t get_cycles_sync(void)
unsigned eax;
/*
+ * Use RDTSCP if possible; it is guaranteed to be synchronous
+ * and doesn't cause a VMEXIT on Hypervisors
+ */
+ alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
+ "=A" (ret), "0" (0ULL) : "ecx", "memory");
+ if (ret)
+ return ret;
+
+ /*
* Don't do an additional sync on CPUs where we know
* RDTSC is already synchronous:
*/
-
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