From 7d27558c4138ac6b3684dea35c2f4379b940a7dd Mon Sep 17 00:00:00 2001 From: john stultz Date: Fri, 1 May 2009 13:10:26 -0700 Subject: timekeeping: create arch_gettimeoffset infrastructure Some arches don't supply their own clocksource. This is mainly the case in architectures that get their inter-tick times by reading the counter on their interval timer. Since these timers wrap every tick, they're not really useful as clocksources. Wrapping them to act like one is possible but not very efficient. So we provide a callout these arches can implement for use with the jiffies clocksource to provide finer then tick granular time. [ Impact: ease the migration to generic time keeping ] Signed-off-by: John Stultz Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/time/timekeeping.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'kernel/time/timekeeping.c') diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 687dff49f6e7..e97c50f8458b 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -77,6 +77,10 @@ static void clocksource_forward_now(void) clock->cycle_last = cycle_now; nsec = cyc2ns(clock, cycle_delta); + + /* If arch requires, add in gettimeoffset() */ + nsec += arch_gettimeoffset(); + timespec_add_ns(&xtime, nsec); nsec = ((s64)cycle_delta * clock->mult_orig) >> clock->shift; @@ -111,6 +115,9 @@ void getnstimeofday(struct timespec *ts) /* convert to nanoseconds: */ nsecs = cyc2ns(clock, cycle_delta); + /* If arch requires, add in gettimeoffset() */ + nsecs += arch_gettimeoffset(); + } while (read_seqretry(&xtime_lock, seq)); timespec_add_ns(ts, nsecs); -- cgit v1.2.3 From dce48a84adf1806676319f6f480e30a6daa012f9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 11 Apr 2009 10:43:41 +0200 Subject: sched, timers: move calc_load() to scheduler Dimitri Sivanich noticed that xtime_lock is held write locked across calc_load() which iterates over all online CPUs. That can cause long latencies for xtime_lock readers on large SMP systems. The load average calculation is an rough estimate anyway so there is no real need to protect the readers vs. the update. It's not a problem when the avenrun array is updated while a reader copies the values. Instead of iterating over all online CPUs let the scheduler_tick code update the number of active tasks shortly before the avenrun update happens. The avenrun update itself is handled by the CPU which calls do_timer(). [ Impact: reduce xtime_lock write locked section ] Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/time/timekeeping.c') diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 687dff49f6e7..52a8bf8931f3 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -22,7 +22,7 @@ /* * This read-write spinlock protects us from races in SMP while - * playing with xtime and avenrun. + * playing with xtime. */ __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock); -- cgit v1.2.3