[tip:sched/urgent] sched/x86/tsc: Initialize multiplier to 0

From: tip-bot for Peter Zijlstra
Date: Thu Jan 23 2014 - 11:47:50 EST

Commit-ID: 5e3c1afd4587e70c201bf7224b51f747c9a3dfa8
Gitweb: http://git.kernel.org/tip/5e3c1afd4587e70c201bf7224b51f747c9a3dfa8
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Wed, 22 Jan 2014 22:08:14 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 23 Jan 2014 14:48:36 +0100

sched/x86/tsc: Initialize multiplier to 0

Since we keep the clock value linearly continuous on frequency change,
make sure the initial multiplier is 0, such that our initial value is 0.
Without this we compute the initial value at whatever the TSC has
managed to reach since power-on.

Reported-and-Tested-by: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
Fixes: 20d1c86a57762 ("sched/clock, x86: Rewrite cyc2ns() to avoid the need to disable IRQs")
Cc: lenb@xxxxxxxxxx
Cc: rjw@xxxxxxxxxxxxx
Cc: Eliezer Tamir <eliezer.tamir@xxxxxxxxxxxxxxx>
Cc: rui.zhang@xxxxxxxxx
Cc: jacob.jun.pan@xxxxxxxxxxxxxxx
Cc: Mike Galbraith <bitbucket@xxxxxxxxx>
Cc: hpa@xxxxxxxxx
Cc: paulmck@xxxxxxxxxxxxxxxxxx
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: dyoung@xxxxxxxxxx
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20140123094804.GP30183@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
arch/x86/kernel/tsc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index a3acbac..19e5adb 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -180,7 +180,7 @@ static void cyc2ns_write_end(int cpu, struct cyc2ns_data *data)

static void cyc2ns_data_init(struct cyc2ns_data *data)
- data->cyc2ns_mul = 1U << CYC2NS_SCALE_FACTOR;
+ data->cyc2ns_mul = 0;
data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
data->cyc2ns_offset = 0;
data->__count = 0;
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