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x86/tsc: Fix sched_clock() sync 

While looking through the code I noticed that we initialize the cyc2ns
fields with a different cycle value for each CPU, resulting in a
slightly different 0 point for each CPU.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2017-05-05 09:55:01 +02:00 committed by Ingo Molnar
parent 59eaef78bf
commit 615cd03373
1 changed files with 11 additions and 5 deletions
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16
arch/x86/kernel/tsc.c
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@ -137,9 +137,9 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
return ns;
}
static void set_cyc2ns_scale(unsigned long khz, int cpu)
static void __set_cyc2ns_scale(unsigned long khz, int cpu, unsigned long long tsc_now)
{
unsigned long long tsc_now, ns_now;
unsigned long long ns_now;
struct cyc2ns_data data;
struct cyc2ns *c2n;
unsigned long flags;
@ -150,7 +150,6 @@ static void set_cyc2ns_scale(unsigned long khz, int cpu)
if (!khz)
goto done;
tsc_now = rdtsc();
ns_now = cycles_2_ns(tsc_now);
/*
@ -186,6 +185,12 @@ static void set_cyc2ns_scale(unsigned long khz, int cpu)
sched_clock_idle_wakeup_event(0);
local_irq_restore(flags);
}
static void set_cyc2ns_scale(unsigned long khz, int cpu)
{
__set_cyc2ns_scale(khz, cpu, rdtsc());
}
/*
* Scheduler clock - returns current time in nanosec units.
*/
@ -1251,7 +1256,7 @@ device_initcall(init_tsc_clocksource);
void __init tsc_init(void)
{
u64 lpj;
u64 lpj, cyc;
int cpu;
if (!boot_cpu_has(X86_FEATURE_TSC)) {
@ -1291,9 +1296,10 @@ void __init tsc_init(void)
* speed as the bootup CPU. (cpufreq notifiers will fix this
* up if their speed diverges)
*/
cyc = rdtsc();
for_each_possible_cpu(cpu) {
cyc2ns_init(cpu);
set_cyc2ns_scale(tsc_khz, cpu);
__set_cyc2ns_scale(tsc_khz, cpu, cyc);
}
if (tsc_disabled > 0)