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@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1707110737530.8746@file01.intranet.prod.int.rdu2.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bb5abe8f5fd46c17ca7c27361cbdb99e00db645f..3b9e220621f83c8a5161e8b57b297233370f72ea 100644 (file)
--- 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();