Messages in this thread Patch in this message | | | Date | Tue, 2 Jun 2009 16:17:18 +0900 | From | Paul Mundt <> | Subject | [PATCH] sched: sched_clock() clocksource handling. |
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As there was no additional feedback on the most recent version of this patch, I'm resubmitting it for inclusion. As far as I know there are no more outstanding concerns.
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sched: sched_clock() clocksource handling.
There are presently a number of issues and limitations with how the clocksource and sched_clock() interaction works today. Configurations tend to be grouped in to one of the following:
- Platform provides a clocksource unsuitable for sched_clock() and prefers to use the generic jiffies-backed implementation.
- Platform provides its own clocksource and sched_clock() that wraps in to it.
- Platform uses a generic clocksource (ie, drivers/clocksource/) combined with the generic jiffies-backed sched_clock().
- Platform supports multiple sched_clock()-capable clocksources.
This patch adds a new CLOCK_SOURCE_USE_FOR_SCHED_CLOCK flag to address these issues, which can be set for any sched_clock()-capable clocksource.
The generic sched_clock() implementation is likewise switched over to always read from a designated sched_clocksource, which is default initialized to the jiffies clocksource and updated based on the availability of CLOCK_SOURCE_USE_FOR_SCHED_CLOCK sources. As this uses the generic cyc2ns() logic on the clocksource ->read(), most of the platform-specific sched_clock() implementations can subsequently be killed off.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
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include/linux/clocksource.h | 4 +++- kernel/sched_clock.c | 13 +++++++++++-- kernel/time/clocksource.c | 19 +++++++++++++++++++ kernel/time/jiffies.c | 2 +- 4 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index c56457c..2109940 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -202,7 +202,8 @@ struct clocksource { #endif }; -extern struct clocksource *clock; /* current clocksource */ +extern struct clocksource *clock; /* current clocksource */ +extern struct clocksource *sched_clocksource; /* sched_clock() clocksource */ /* * Clock source flags bits:: @@ -212,6 +213,7 @@ extern struct clocksource *clock; /* current clocksource */ #define CLOCK_SOURCE_WATCHDOG 0x10 #define CLOCK_SOURCE_VALID_FOR_HRES 0x20 +#define CLOCK_SOURCE_USE_FOR_SCHED_CLOCK 0x40 /* simplify initialization of mask field */ #define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1) diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index e1d16c9..b51d48d 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -30,6 +30,8 @@ #include <linux/percpu.h> #include <linux/ktime.h> #include <linux/sched.h> +#include <linux/clocksource.h> +#include <linux/rcupdate.h> /* * Scheduler clock - returns current time in nanosec units. @@ -38,8 +40,15 @@ */ unsigned long long __attribute__((weak)) sched_clock(void) { - return (unsigned long long)(jiffies - INITIAL_JIFFIES) - * (NSEC_PER_SEC / HZ); + unsigned long long time; + struct clocksource *clock; + + rcu_read_lock(); + clock = rcu_dereference(sched_clocksource); + time = cyc2ns(clock, clocksource_read(clock)); + rcu_read_unlock(); + + return time; } static __read_mostly int sched_clock_running; diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 80189f6..3795954 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -25,6 +25,7 @@ */ #include <linux/clocksource.h> +#include <linux/rcupdate.h> #include <linux/sysdev.h> #include <linux/init.h> #include <linux/module.h> @@ -109,6 +110,7 @@ EXPORT_SYMBOL(timecounter_cyc2time); /* XXX - Would like a better way for initializing curr_clocksource */ extern struct clocksource clocksource_jiffies; +struct clocksource *sched_clocksource = &clocksource_jiffies; /*[Clocksource internal variables]--------- * curr_clocksource: @@ -362,6 +364,9 @@ static struct clocksource *select_clocksource(void) if (next == curr_clocksource) return NULL; + if (next->flags & CLOCK_SOURCE_USE_FOR_SCHED_CLOCK) + sched_clocksource = next; + return next; } @@ -440,7 +445,21 @@ void clocksource_unregister(struct clocksource *cs) list_del(&cs->list); if (clocksource_override == cs) clocksource_override = NULL; + next_clocksource = select_clocksource(); + + /* + * If select_clocksource() fails to find another suitable + * clocksource for sched_clocksource and we are unregistering + * it, switch back to jiffies. + */ + if (sched_clocksource == cs) { + rcu_assign_pointer(sched_clocksource, &clocksource_jiffies); + spin_unlock_irqrestore(&clocksource_lock, flags); + synchronize_rcu(); + return; + } + spin_unlock_irqrestore(&clocksource_lock, flags); } diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c index c3f6c30..727d881 100644 --- a/kernel/time/jiffies.c +++ b/kernel/time/jiffies.c @@ -52,7 +52,7 @@ static cycle_t jiffies_read(struct clocksource *cs) { - return (cycle_t) jiffies; + return (cycle_t) (jiffies - INITIAL_JIFFIES); } struct clocksource clocksource_jiffies = {
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