Messages in this thread Patch in this message | | | Date | Thu, 28 May 2009 21:42:07 +0900 | From | Paul Mundt <> | Subject | Re: [PATCH] sched: Support current clocksource handling in fallback sched_clock(). |
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On Thu, May 28, 2009 at 02:22:17PM +0200, Thomas Gleixner wrote: > On Thu, 28 May 2009, Paul Mundt wrote: > > @@ -437,10 +441,19 @@ void clocksource_unregister(struct clocksource *cs) > > unsigned long flags; > > > > spin_lock_irqsave(&clocksource_lock, flags); > > + > > + if (sched_clocksource == cs) { > > + printk(KERN_WARNING "Refusing to unregister " > > + "scheduler clocksource %s", cs->name); > > Hmm, isn't that dangerous ? The clocksource might be in a module or > in kmalloced memory which is going to be freed. > Perhaps the saner thing to do is see if select_clocksource() manages to find something suitable, otherwise switch back to jiffies..
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include/linux/clocksource.h | 4 +++- kernel/sched_clock.c | 6 ++++-- kernel/time/clocksource.c | 14 ++++++++++++++ kernel/time/jiffies.c | 2 +- 4 files changed, 22 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..b91190e 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -30,6 +30,7 @@ #include <linux/percpu.h> #include <linux/ktime.h> #include <linux/sched.h> +#include <linux/clocksource.h> /* * Scheduler clock - returns current time in nanosec units. @@ -38,8 +39,9 @@ */ unsigned long long __attribute__((weak)) sched_clock(void) { - return (unsigned long long)(jiffies - INITIAL_JIFFIES) - * (NSEC_PER_SEC / HZ); + struct clocksource *clock = ACCESS_ONCE(sched_clocksource); + + return cyc2ns(clock, clocksource_read(clock)); } static __read_mostly int sched_clock_running; diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 80189f6..19c72d0 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -109,6 +109,7 @@ 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 +363,9 @@ 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 +444,17 @@ 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) + sched_clocksource = &clocksource_jiffies; + 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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