Messages in this thread Patch in this message | | | Date | Thu, 28 May 2009 18:19:36 +0900 | From | Paul Mundt <> | Subject | Re: [PATCH] sched: Support current clocksource handling in fallback sched_clock(). |
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On Wed, May 27, 2009 at 09:25:25AM -0700, Daniel Walker wrote: > On Wed, 2009-05-27 at 09:15 +0900, Paul Mundt wrote: > > > unsigned long long __attribute__((weak)) sched_clock(void) > > { > > + /* > > + * Use the current clocksource when it becomes available later in > > + * the boot process, and ensure that it is usable for sched_clock(). > > + */ > > + if (clock && (clock->flags & CLOCK_SOURCE_USE_FOR_SCHED_CLOCK)) > > + return cyc2ns(clock, clocksource_read(clock)); > > + > > + /* Otherwise just fall back on jiffies */ > > return (unsigned long long)(jiffies - INITIAL_JIFFIES) > > Do we really need all this complexity in a fast path? the jiffies > clocksource is static and always ready. Could we instead remove the > usage of "clock" and create a new pointer called "sched_clocksource" and > initialize it to the jiffies clock, and allow the clocksource management > code to update that new pointer based on the > CLOCK_SOURCE_USE_FOR_SCHED_CLOCK flag when new clocksources are > registered/removed/marked unstable etc.. > > that would eliminate all the code in sched_clock except one line, > > unsigned long long __attribute__((weak)) sched_clock(void) > { > return cyc2ns(sched_clocksource, clocksource_read(sched_clocksource)); > } > Ok, there were some ordering problems with the early platform code, but I've played with this a bit more and got it to the point where this now also works. I can live with this over the v3 version if people prefer this approach instead.
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include/linux/clocksource.h | 4 +++- kernel/sched_clock.c | 4 ++-- kernel/time/clocksource.c | 4 ++++ kernel/time/jiffies.c | 2 +- 4 files changed, 10 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..c06c285 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 +39,7 @@ */ unsigned long long __attribute__((weak)) sched_clock(void) { - return (unsigned long long)(jiffies - INITIAL_JIFFIES) - * (NSEC_PER_SEC / HZ); + return cyc2ns(sched_clocksource, clocksource_read(sched_clocksource)); } static __read_mostly int sched_clock_running; diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 80189f6..d148a75 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; } 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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