[tip:x86/urgent] x86/cpu: Use indirect call to measure performance in init_amd_k6()
From: tip-bot for Mikulas Patocka
Date: Sun Jul 16 2017 - 05:20:20 EST
Commit-ID: 5f8a16156aa1b2d0223eaee9dacdfb9bc096f610
Gitweb: http://git.kernel.org/tip/5f8a16156aa1b2d0223eaee9dacdfb9bc096f610
Author: Mikulas Patocka <mpatocka@xxxxxxxxxx>
AuthorDate: Tue, 11 Jul 2017 07:44:05 -0400
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sun, 16 Jul 2017 11:05:04 +0200
x86/cpu: Use indirect call to measure performance in init_amd_k6()
This old piece of code is supposed to measure the performance of indirect
calls to determine if the processor is buggy or not, however the compiler
optimizer turns it into a direct call.
Use the OPTIMIZER_HIDE_VAR() macro to thwart the optimization, so that a real
indirect call is generated.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1707110737530.8746@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/cpu/amd.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bb5abe8..3b9e220 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -134,6 +134,7 @@ static void init_amd_k6(struct cpuinfo_x86 *c)
n = K6_BUG_LOOP;
f_vide = vide;
+ OPTIMIZER_HIDE_VAR(f_vide);
d = rdtsc();
while (n--)
f_vide();