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-rw-r--r--arch/x86/kernel/cpu/intel.c8
-rw-r--r--include/linux/sched.h10
-rw-r--r--kernel/sched_clock.c47
3 files changed, 40 insertions, 25 deletions
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 24ff26a..5fff00c 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -4,6 +4,7 @@
#include <linux/string.h>
#include <linux/bitops.h>
#include <linux/smp.h>
+#include <linux/sched.h>
#include <linux/thread_info.h>
#include <linux/module.h>
@@ -56,11 +57,16 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
/*
* c->x86_power is 8000_0007 edx. Bit 8 is TSC runs at constant rate
- * with P/T states and does not stop in deep C-states
+ * with P/T states and does not stop in deep C-states.
+ *
+ * It is also reliable across cores and sockets. (but not across
+ * cabinets - we turn it off in that case explicitly.)
*/
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
+ set_cpu_cap(c, X86_FEATURE_TSC_RELIABLE);
+ sched_clock_stable = 1;
}
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 426666d..7702cb1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1672,6 +1672,16 @@ static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)
return set_cpus_allowed_ptr(p, &new_mask);
}
+/*
+ * Architectures can set this to 1 if they have specified
+ * CONFIG_HAVE_UNSTABLE_SCHED_CLOCK in their arch Kconfig,
+ * but then during bootup it turns out that sched_clock()
+ * is reliable after all:
+ */
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+extern int sched_clock_stable;
+#endif
+
extern unsigned long long sched_clock(void);
extern void sched_clock_init(void);
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index db69174..7ec82c1 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -24,12 +24,12 @@
* The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
* consistent between cpus (never more than 2 jiffies difference).
*/
-#include <linux/sched.h>
-#include <linux/percpu.h>
#include <linux/spinlock.h>
-#include <linux/ktime.h>
-#include <linux/module.h>
#include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/ktime.h>
+#include <linux/sched.h>
/*
* Scheduler clock - returns current time in nanosec units.
@@ -44,6 +44,10 @@ unsigned long long __attribute__((weak)) sched_clock(void)
static __read_mostly int sched_clock_running;
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+__read_mostly int sched_clock_stable;
+#else
+static const int sched_clock_stable = 1;
+#endif
struct sched_clock_data {
/*
@@ -88,7 +92,7 @@ void sched_clock_init(void)
}
/*
- * min,max except they take wrapping into account
+ * min, max except they take wrapping into account
*/
static inline u64 wrap_min(u64 x, u64 y)
@@ -117,10 +121,13 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
if (unlikely(delta < 0))
delta = 0;
+ if (unlikely(!sched_clock_running))
+ return 0ull;
+
/*
* scd->clock = clamp(scd->tick_gtod + delta,
- * max(scd->tick_gtod, scd->clock),
- * scd->tick_gtod + TICK_NSEC);
+ * max(scd->tick_gtod, scd->clock),
+ * scd->tick_gtod + TICK_NSEC);
*/
clock = scd->tick_gtod + delta;
@@ -149,8 +156,13 @@ static void lock_double_clock(struct sched_clock_data *data1,
u64 sched_clock_cpu(int cpu)
{
- struct sched_clock_data *scd = cpu_sdc(cpu);
u64 now, clock, this_clock, remote_clock;
+ struct sched_clock_data *scd;
+
+ if (sched_clock_stable)
+ return sched_clock();
+
+ scd = cpu_sdc(cpu);
/*
* Normally this is not called in NMI context - but if it is,
@@ -201,6 +213,8 @@ u64 sched_clock_cpu(int cpu)
return clock;
}
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+
void sched_clock_tick(void)
{
struct sched_clock_data *scd = this_scd();
@@ -243,22 +257,7 @@ void sched_clock_idle_wakeup_event(u64 delta_ns)
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
-#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
-
-void sched_clock_init(void)
-{
- sched_clock_running = 1;
-}
-
-u64 sched_clock_cpu(int cpu)
-{
- if (unlikely(!sched_clock_running))
- return 0;
-
- return sched_clock();
-}
-
-#endif
+#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
unsigned long long cpu_clock(int cpu)
{
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