Commit-ID: 615cd03373a02a17b82b253ff5e02e3a83b224f8
Gitweb: http://git.kernel.org/tip/615cd03373a02a17b82b253ff5e02e3a83b224f8
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Fri, 5 May 2017 09:55:01 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 15 May 2017 10:15:16 +0200
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@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/tsc.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 23ce8b9..dda964c 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -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 @@ done:
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)
--
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