linux-kernel - [PATCH 03/10] x86/asm: Tweak the comment about wmb() use for IO

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Date:	Tue, 26 Jan 2016 22:12:03 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 03/10] x86/asm: Tweak the comment about wmb() use for IO

From: "Michael S. Tsirkin" <mst@...hat.com>

On x86, we *do* still use the non-nop rmb()/wmb() for IO barriers, but
even that is generally questionable.

Leave them around for historical reasons, unless somebody can point to a
case where they care about the performance. Tweak the comment so people
don't think they are strictly required in all cases.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Cc: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: virtualization <virtualization@...ts.linux-foundation.org>
Link: http://lkml.kernel.org/r/1452715911-12067-4-git-send-email-mst@redhat.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/include/asm/barrier.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index d2aa66a3a4b5..4f95b2affd88 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -6,8 +6,8 @@
 
 /*
  * Force strict CPU ordering.
- * And yes, this is required on UP too when we're talking
- * to devices.
+ *
+ * And yes, this might be required on UP too when we're talking to devices.
  */
 
 #ifdef CONFIG_X86_32
-- 
2.3.5