Messages in this thread | | | Subject | Re: [RFC-PATCH] clocksource: update lpj if clocksource has been changed. | From | john stultz <> | Date | Thu, 11 Nov 2010 12:02:41 -0800 |
| |
On Thu, 2010-11-11 at 17:36 +0900, MyungJoo Ham wrote: > With a clocksource change, loops_per_jiffy may have been changed; thus, > the loops_per_jiffy in each cpu should be updated. Especially after some > of the cpus were turned off and on, their loops_per_jiffy values are > updated while the cpus kept on are not. Therefore, in order to make them > "normalized equally", we need to let the loops_per_jiffy values of > different cpus be based on the same clocksource. > > Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com> > Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
First, Thanks for reporting the issue and submitting the patch!
So the premise is that read_current_timer -> get_cycles -> clocksource_read on some arches. And then when we select a different clocksource for timekeeping, this also changes the get_cycles source breaking delay loops.
The clocksource selected for timekeeping and the counter being used for get_cycles really shouldn't be explicitly bound. On most systems I don't think that is the case, so this patch would force needless recalibration calls on clocksource changes.
Which arch specifically are you seeing the issue on? I suspect there is be a better way to fix this.
thanks -john
> --- > kernel/time/clocksource.c | 13 +++++++++++++ > 1 files changed, 13 insertions(+), 0 deletions(-) > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index c18d7ef..a9d7935 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -30,6 +30,9 @@ > #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */ > #include <linux/tick.h> > #include <linux/kthread.h> > +#include <linux/delay.h> > > void timecounter_init(struct timecounter *tc, > const struct cyclecounter *cc, > @@ -592,6 +593,9 @@ static inline void clocksource_select(void) { } > */ > static int __init clocksource_done_booting(void) > { > +#ifdef CONFIG_SMP > + int cpu; > +#endif > mutex_lock(&clocksource_mutex); > curr_clocksource = clocksource_default_clock(); > mutex_unlock(&clocksource_mutex); > @@ -606,6 +610,13 @@ static int __init clocksource_done_booting(void) > mutex_lock(&clocksource_mutex); > clocksource_select(); > mutex_unlock(&clocksource_mutex); > + > + calibrate_delay(); > +#ifdef CONFIG_SMP > + /* loops_per_jiffy may have been changed. */ > + for_each_online_cpu(cpu) > + smp_store_cpu_info(cpu); > +#endif > return 0; > } > fs_initcall(clocksource_done_booting);
| |