Hi Julien, On Fri, 2020-06-12 at 13:45 +0100, Julien Grall wrote: > Hi Volodymyr, > > On 12/06/2020 12:44, Volodymyr Babchuk wrote: > > On Fri, 2020-06-12 at 06:57 +0200, Jürgen Groß wrote: > > > On 12.06.20 02:22, Volodymyr Babchuk wrote: > > > > As scheduler code now collects time spent in IRQ handlers and in > > > > do_softirq(), we can present those values to userspace tools like > > > > xentop, so system administrator can see how system behaves. > > > > > > > > We are updating counters only in sched_get_time_correction() function > > > > to minimize number of taken spinlocks. As atomic_t is 32 bit wide, it > > > > is not enough to store time with nanosecond precision. So we need to > > > > use 64 bit variables and protect them with spinlock. > > > > > > > > Signed-off-by: Volodymyr Babchuk <volodymyr_babc...@epam.com> > > > > --- > > > > xen/common/sched/core.c | 17 +++++++++++++++++ > > > > xen/common/sysctl.c | 1 + > > > > xen/include/public/sysctl.h | 4 +++- > > > > xen/include/xen/sched.h | 2 ++ > > > > 4 files changed, 23 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c > > > > index a7294ff5c3..ee6b1d9161 100644 > > > > --- a/xen/common/sched/core.c > > > > +++ b/xen/common/sched/core.c > > > > @@ -95,6 +95,10 @@ static struct scheduler __read_mostly ops; > > > > > > > > static bool scheduler_active; > > > > > > > > +static DEFINE_SPINLOCK(sched_stat_lock); > > > > +s_time_t sched_stat_irq_time; > > > > +s_time_t sched_stat_hyp_time; > > > > + > > > > static void sched_set_affinity( > > > > struct sched_unit *unit, const cpumask_t *hard, const cpumask_t > > > > *soft); > > > > > > > > @@ -994,9 +998,22 @@ s_time_t sched_get_time_correction(struct > > > > sched_unit *u) > > > > break; > > > > } > > > > > > > > + spin_lock_irqsave(&sched_stat_lock, flags); > > > > + sched_stat_irq_time += irq; > > > > + sched_stat_hyp_time += hyp; > > > > + spin_unlock_irqrestore(&sched_stat_lock, flags); > > > > > > Please don't use a lock. Just use add_sized() instead which will add > > > atomically. > > > > Looks like arm does not support 64 bit variables. > > > Julien, I believe, this is armv7 limitation? Should armv8 work with 64- > > bit atomics? > > 64-bit atomics can work on both Armv7 and Armv8 :). It just haven't been > plumbed yet.
Wow, didn't know that armv7 is capable of that. > I am happy to write a patch if you need atomic64_t or even a 64-bit > add_sized(). That would be cool. Certainly. But looks like x86 code does not have implementation for atomic64_t as well. So, there would be lots of changes just for one use case. I don't know if it is worth it. Let's finish discussion of other parts of the series. If it will appear that atomic64_t is absolutely necessay, I'll return back to you. Thanks for offer anyways.
