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Commit 615cd033 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 59eaef78

arch/x86/kernel/tsc.c

+11 −5
Original line number Diff line number Diff line
@@ -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)