linux-kernel - [PATCH 3/3] pvclock: Add a new wrapper function to only get variable flags

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Date:	Fri, 27 May 2016 14:17:12 +0800
From:	Minfei Huang <mnghuan@...il.com>
To:	bp@...e.de, pbonzini@...hat.com, luto@...nel.org, hpa@...or.com,
	mingo@...hat.com, tglx@...utronix.de
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Minfei Huang <mnghuan@...il.com>
Subject: [PATCH 3/3] pvclock: Add a new wrapper function to only get variable flags

There is a generic function __pvclock_read_cycles to be used to get both
flags and cycles. For function pvclock_read_flags, it's useless to get
cycles value. To make this function be more effective, add a new wrapper
function to only get variable flags.

Signed-off-by: Minfei Huang <mnghuan@...il.com>
---
 arch/x86/include/asm/pvclock.h | 12 ++++++++++++
 arch/x86/kernel/pvclock.c      |  3 +--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 7c1c895..3c4e5b7 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -88,6 +88,18 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
 	return version;
 }
 
+static __always_inline unsigned int __pvclock_read_flags(
+		const struct pvclock_vcpu_time_info *src, u8 *flags)
+{
+	unsigned int version;
+
+	version = src->version;
+	/* Make the latest version visible */
+	smp_rmb();
+	*flags = src->flags;
+	return version;
+}
+
 struct pvclock_vsyscall_time_info {
 	struct pvclock_vcpu_time_info pvti;
 } __attribute__((__aligned__(SMP_CACHE_BYTES)));
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 7f82fe0..138772c 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -61,11 +61,10 @@ void pvclock_resume(void)
 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
 {
 	unsigned version;
-	cycle_t ret;
 	u8 flags;
 
 	do {
-		version = __pvclock_read_cycles(src, &ret, &flags);
+		version = __pvclock_read_flags(src, &flags);
 		/* Make sure that the version double-check is last. */
 		smp_rmb();
 	} while ((src->version & 1) || version != src->version);
-- 
2.6.3