Hi Julien, Julien Grall writes:
> On Thu, 18 Jun 2020 at 21:24, Volodymyr Babchuk > <volodymyr_babc...@epam.com> wrote: >> >> >> 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. > > I offered help for either the atomic64_t or the add_sized(). Can you > confirm which one you need? Yes, sorry. I had atomic64_t in mind. -- Volodymyr Babchuk at EPAM
