linux-kernel - [PATCH 4/4] x86: add rdtsc

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Date:	Thu, 14 May 2009 15:07:09 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	linux-kernel@...r.kernel.org, linux-x86_64@...r.kernel.org,
	mingo@...e.hu, andi@...stfloor.org
Cc:	zwane@....linux.org.uk, roland@...hat.com,
	Petr Tesarik <ptesarik@...e.cz>
Subject: [PATCH 4/4] x86: add rdtsc_barrier() to vgetns()

Commit cb9e35dce94a1b9c59d46224e8a94377d673e204 removed
rdtsc_barrier() from vget_cycles() and moved it to
do_vgettimeofday().

AFAICS the same is also needed for vgetns(), because it may
call vread_tsc(), which in turn reads the TSC counter
using vget_cycles().

Signed-off-by: Petr Tesarik <ptesarik@...e.cz>
---
 arch/x86/vdso/vclock_gettime.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 6a40b78..ab1ae6c 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -36,11 +36,14 @@ notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 
 notrace static inline long vgetns(void)
 {
-	long v;
-	cycles_t (*vread)(void);
+	cycle_t now, cycle_delta;
+	cycle_t (*vread)(void);
 	vread = gtod->clock.vread;
-	v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
-	return (v * gtod->clock.mult) >> gtod->clock.shift;
+	rdtsc_barrier();
+	now = vread();
+	rdtsc_barrier();
+	cycle_delta = (now - gtod->clock.cycle_last) & gtod->clock.mask;
+	return (cycle_delta * gtod->clock.mult) >> gtod->clock.shift;
 }
 
 notrace static noinline int do_realtime(struct timespec *ts)
-- 
1.6.0.2


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