lkml.org 
[lkml]   [2017]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:x86/urgent] x86/cpu: Use indirect call to measure performance in init_amd_k6()
Commit-ID:  429ed86b5c99b388543f6f7f6983b1230326f2bb
Gitweb: http://git.kernel.org/tip/429ed86b5c99b388543f6f7f6983b1230326f2bb
Author: Mikulas Patocka <mpatocka@redhat.com>
AuthorDate: Tue, 11 Jul 2017 07:44:05 -0400
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 12 Jul 2017 10:42:32 +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@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>
---
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();
\
 
 \ /
  Last update: 2017-07-12 15:17    [W:0.085 / U:0.344 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site