sched_clock: Add local_clock() API and improve documentation

For people who otherwise get to write: cpu_clock(smp_processor_id()),
there is now: local_clock().

Also, as per suggestion from Andrew, provide some documentation on
the various clock interfaces, and minimize the unsigned long long vs
u64 mess.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <jaxboe@fusionio.com>
LKML-Reference: <1275052414.1645.52.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2010-05-25 10:48:51 +02:00 committed by Ingo Molnar
parent 95ae3c59fa
commit c676329abb
8 changed files with 113 additions and 34 deletions

View file

@ -82,7 +82,7 @@ unsigned long ftrace_return_to_handler(unsigned long retval0,
unsigned long ret;
pop_return_trace(&trace, &ret);
trace.rettime = cpu_clock(raw_smp_processor_id());
trace.rettime = local_clock();
ftrace_graph_return(&trace);
if (unlikely(!ret)) {
@ -126,7 +126,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
return;
}
calltime = cpu_clock(raw_smp_processor_id());
calltime = local_clock();
if (push_return_trace(old, calltime,
self_addr, &trace.depth) == -EBUSY) {

View file

@ -1791,20 +1791,23 @@ static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)
#endif
/*
* 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:
* Do not use outside of architecture code which knows its limitations.
*
* sched_clock() has no promise of monotonicity or bounded drift between
* CPUs, use (which you should not) requires disabling IRQs.
*
* Please use one of the three interfaces below.
*/
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
extern int sched_clock_stable;
#endif
/* ftrace calls sched_clock() directly */
extern unsigned long long notrace sched_clock(void);
/*
* See the comment in kernel/sched_clock.c
*/
extern u64 cpu_clock(int cpu);
extern u64 local_clock(void);
extern u64 sched_clock_cpu(int cpu);
extern void sched_clock_init(void);
extern u64 sched_clock_cpu(int cpu);
#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
static inline void sched_clock_tick(void)
@ -1819,17 +1822,19 @@ static inline void sched_clock_idle_wakeup_event(u64 delta_ns)
{
}
#else
/*
* 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:
*/
extern int sched_clock_stable;
extern void sched_clock_tick(void);
extern void sched_clock_idle_sleep_event(void);
extern void sched_clock_idle_wakeup_event(u64 delta_ns);
#endif
/*
* For kernel-internal use: high-speed (but slightly incorrect) per-cpu
* clock constructed from sched_clock():
*/
extern unsigned long long cpu_clock(int cpu);
extern unsigned long long
task_sched_runtime(struct task_struct *task);
extern unsigned long long thread_group_sched_runtime(struct task_struct *task);

View file

@ -146,7 +146,7 @@ static DEFINE_PER_CPU(struct lock_class_stats[MAX_LOCKDEP_KEYS],
static inline u64 lockstat_clock(void)
{
return cpu_clock(smp_processor_id());
return local_clock();
}
static int lock_point(unsigned long points[], unsigned long ip)

View file

@ -214,7 +214,7 @@ static void perf_unpin_context(struct perf_event_context *ctx)
static inline u64 perf_clock(void)
{
return cpu_clock(raw_smp_processor_id());
return local_clock();
}
/*

View file

@ -239,8 +239,7 @@ static unsigned long
rcu_random(struct rcu_random_state *rrsp)
{
if (--rrsp->rrs_count < 0) {
rrsp->rrs_state +=
(unsigned long)cpu_clock(raw_smp_processor_id());
rrsp->rrs_state += (unsigned long)local_clock();
rrsp->rrs_count = RCU_RANDOM_REFRESH;
}
rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;

View file

@ -1647,7 +1647,7 @@ static void update_shares(struct sched_domain *sd)
if (root_task_group_empty())
return;
now = cpu_clock(raw_smp_processor_id());
now = local_clock();
elapsed = now - sd->last_update;
if (elapsed >= (s64)(u64)sysctl_sched_shares_ratelimit) {

View file

@ -10,19 +10,55 @@
* Ingo Molnar <mingo@redhat.com>
* Guillaume Chazarain <guichaz@gmail.com>
*
* Create a semi stable clock from a mixture of other events, including:
* - gtod
*
* What:
*
* cpu_clock(i) provides a fast (execution time) high resolution
* clock with bounded drift between CPUs. The value of cpu_clock(i)
* is monotonic for constant i. The timestamp returned is in nanoseconds.
*
* ######################### BIG FAT WARNING ##########################
* # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
* # go backwards !! #
* ####################################################################
*
* There is no strict promise about the base, although it tends to start
* at 0 on boot (but people really shouldn't rely on that).
*
* cpu_clock(i) -- can be used from any context, including NMI.
* sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI)
* local_clock() -- is cpu_clock() on the current cpu.
*
* How:
*
* The implementation either uses sched_clock() when
* !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
* sched_clock() is assumed to provide these properties (mostly it means
* the architecture provides a globally synchronized highres time source).
*
* Otherwise it tries to create a semi stable clock from a mixture of other
* clocks, including:
*
* - GTOD (clock monotomic)
* - sched_clock()
* - explicit idle events
*
* We use gtod as base and the unstable clock deltas. The deltas are filtered,
* making it monotonic and keeping it within an expected window.
* We use GTOD as base and use sched_clock() deltas to improve resolution. The
* deltas are filtered to provide monotonicity and keeping it within an
* expected window.
*
* Furthermore, explicit sleep and wakeup hooks allow us to account for time
* that is otherwise invisible (TSC gets stopped).
*
* The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
* consistent between cpus (never more than 2 jiffies difference).
*
* Notes:
*
* The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things
* like cpufreq interrupts that can change the base clock (TSC) multiplier
* and cause funny jumps in time -- although the filtering provided by
* sched_clock_cpu() should mitigate serious artifacts we cannot rely on it
* in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on
* sched_clock().
*/
#include <linux/spinlock.h>
#include <linux/hardirq.h>
@ -170,6 +206,11 @@ static u64 sched_clock_remote(struct sched_clock_data *scd)
return val;
}
/*
* Similar to cpu_clock(), but requires local IRQs to be disabled.
*
* See cpu_clock().
*/
u64 sched_clock_cpu(int cpu)
{
struct sched_clock_data *scd;
@ -237,9 +278,19 @@ void sched_clock_idle_wakeup_event(u64 delta_ns)
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
unsigned long long cpu_clock(int cpu)
/*
* As outlined at the top, provides a fast, high resolution, nanosecond
* time source that is monotonic per cpu argument and has bounded drift
* between cpus.
*
* ######################### BIG FAT WARNING ##########################
* # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
* # go backwards !! #
* ####################################################################
*/
u64 cpu_clock(int cpu)
{
unsigned long long clock;
u64 clock;
unsigned long flags;
local_irq_save(flags);
@ -249,6 +300,25 @@ unsigned long long cpu_clock(int cpu)
return clock;
}
/*
* Similar to cpu_clock() for the current cpu. Time will only be observed
* to be monotonic if care is taken to only compare timestampt taken on the
* same CPU.
*
* See cpu_clock().
*/
u64 local_clock(void)
{
u64 clock;
unsigned long flags;
local_irq_save(flags);
clock = sched_clock_cpu(smp_processor_id());
local_irq_restore(flags);
return clock;
}
#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
void sched_clock_init(void)
@ -264,12 +334,17 @@ u64 sched_clock_cpu(int cpu)
return sched_clock();
}
unsigned long long cpu_clock(int cpu)
u64 cpu_clock(int cpu)
{
return sched_clock_cpu(cpu);
}
u64 local_clock(void)
{
return sched_clock_cpu(0);
}
#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
EXPORT_SYMBOL_GPL(cpu_clock);
EXPORT_SYMBOL_GPL(local_clock);

View file

@ -56,7 +56,7 @@ u64 notrace trace_clock_local(void)
*/
u64 notrace trace_clock(void)
{
return cpu_clock(raw_smp_processor_id());
return local_clock();
}