Hi Julien, Julien Grall writes:
> 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. > > I am happy to write a patch if you need atomic64_t or even a 64-bit > add_sized(). Looks like I'll need this patch. So, if you still have time, it will be great, if you'll write it. -- Volodymyr Babchuk at EPAM
