linux-kernel - Re: [PATCH -v2 0/8] jump_label: Another (better) static

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Date:	Wed, 29 Jul 2015 08:46:00 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jasonbaron0@...il.com, bp@...en8.de, luto@...capital.net,
	tglx@...utronix.de, rostedt@...dmis.org, will.deacon@....com,
	liuj97@...il.com, rabin@....in, ralf@...ux-mips.org,
	ddaney@...iumnetworks.com, benh@...nel.crashing.org,
	michael@...erman.id.au, davem@...emloft.net, vbabka@...e.cz
Subject: Re: [PATCH -v2 0/8] jump_label: Another (better) static_key interface

On Tue, Jul 28, 2015 at 03:20:55PM +0200, Peter Zijlstra wrote:
> Hi all,
> 
> After yet another bug because of the weirdness of the static key interface,
> here an attempt at providing a better one.
> 
> This series is tested on x86_64 (by me) and s390x (heiko).

Works nice. You may include the s390 patch below, so the conversion to the
new interface happens when your code gets merged:

>From 3c9b5a2b9a90d6bb2b41f381f5f89b3657fe4ea5 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@...ibm.com>
Date: Wed, 29 Jul 2015 08:31:24 +0200
Subject: [PATCH] s390/uaccess: employ static_branch_likely()

Use the new static_branch_likely() primitive to make sure that the
most likely case is executed without taking an unconditional branch.
This wasn't possible with the old jump label primitives.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 arch/s390/lib/uaccess.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/s390/lib/uaccess.c b/arch/s390/lib/uaccess.c
index 4614d415bb58..93cb1d09493d 100644
--- a/arch/s390/lib/uaccess.c
+++ b/arch/s390/lib/uaccess.c
@@ -15,7 +15,7 @@
 #include <asm/mmu_context.h>
 #include <asm/facility.h>
 
-static struct static_key have_mvcos = STATIC_KEY_INIT_FALSE;
+static DEFINE_STATIC_KEY_FALSE(have_mvcos);
 
 static inline unsigned long copy_from_user_mvcos(void *x, const void __user *ptr,
 						 unsigned long size)
@@ -104,7 +104,7 @@ static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
 
 unsigned long __copy_from_user(void *to, const void __user *from, unsigned long n)
 {
-	if (static_key_false(&have_mvcos))
+	if (static_branch_likely(&have_mvcos))
 		return copy_from_user_mvcos(to, from, n);
 	return copy_from_user_mvcp(to, from, n);
 }
@@ -177,7 +177,7 @@ static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
 
 unsigned long __copy_to_user(void __user *to, const void *from, unsigned long n)
 {
-	if (static_key_false(&have_mvcos))
+	if (static_branch_likely(&have_mvcos))
 		return copy_to_user_mvcos(to, from, n);
 	return copy_to_user_mvcs(to, from, n);
 }
@@ -240,7 +240,7 @@ static inline unsigned long copy_in_user_mvc(void __user *to, const void __user
 
 unsigned long __copy_in_user(void __user *to, const void __user *from, unsigned long n)
 {
-	if (static_key_false(&have_mvcos))
+	if (static_branch_likely(&have_mvcos))
 		return copy_in_user_mvcos(to, from, n);
 	return copy_in_user_mvc(to, from, n);
 }
@@ -312,7 +312,7 @@ static inline unsigned long clear_user_xc(void __user *to, unsigned long size)
 
 unsigned long __clear_user(void __user *to, unsigned long size)
 {
-	if (static_key_false(&have_mvcos))
+	if (static_branch_likely(&have_mvcos))
 			return clear_user_mvcos(to, size);
 	return clear_user_xc(to, size);
 }
@@ -386,7 +386,7 @@ early_param("uaccess_primary", parse_uaccess_pt);
 static int __init uaccess_init(void)
 {
 	if (!uaccess_primary && test_facility(27))
-		static_key_slow_inc(&have_mvcos);
+		static_branch_enable(&have_mvcos);
 	return 0;
 }
 early_initcall(uaccess_init);
-- 
2.3.8

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