linux-kernel - [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read

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Message-Id: <1464438463-8485-1-git-send-email-mnghuan@gmail.com>
Date:	Sat, 28 May 2016 20:27:43 +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 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read_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, get this variable
flags directly in function.

Signed-off-by: Minfei Huang <mnghuan@...il.com>
---
v1:
- Get rid of __pvclock_read_cycles according to Andy's suggestion
---
 arch/x86/kernel/pvclock.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 7f82fe0..06c58ce 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -61,11 +61,14 @@ 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 = src->version;
+		/* Make the latest version visible */
+		smp_rmb();
+
+		flags = src->flags;
 		/* Make sure that the version double-check is last. */
 		smp_rmb();
 	} while ((src->version & 1) || version != src->version);
-- 
2.6.3