On Fri, Oct 25, 2013 at 7:44 PM, Jiri Olsa <jo...@redhat.com> wrote:
> On Wed, Oct 23, 2013 at 02:58:05PM +0200, Stephane Eranian wrote:
>> The RAPL PMU counters do not interrupt on overflow.
>> Therefore, the kernel needs to poll the counters
>> to avoid missing an overflow. This patch adds
>> the hrtimer code to do this.
>>
>> The timer internval is calculated at boot time
>> based on the power unit used by the HW.
>>
>> Signed-off-by: Stephane Eranian <eran...@google.com>
>> ---
>> arch/x86/kernel/cpu/perf_event_intel_rapl.c | 75
>> +++++++++++++++++++++++++--
>> 1 file changed, 70 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/perf_event_intel_rapl.c
>> b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
>> index 3d71d39..ed0566a 100644
>> --- a/arch/x86/kernel/cpu/perf_event_intel_rapl.c
>> +++ b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
>> @@ -92,11 +92,13 @@ static struct kobj_attribute format_attr_##_var =
>> \
>>
>> struct rapl_pmu {
>> spinlock_t lock;
>> - atomic_t refcnt;
>> int hw_unit; /* 1/2^hw_unit Joule */
>> - int phys_id;
>> - int n_active; /* number of active events */
>> + struct hrtimer hrtimer;
>> struct list_head active_list;
>> + ktime_t timer_interval; /* in ktime_t unit */
>> + int n_active; /* number of active events */
>> + int phys_id;
>> + atomic_t refcnt;
>> };
>>
>> static struct pmu rapl_pmu_class;
>> @@ -161,6 +163,47 @@ static u64 rapl_event_update(struct perf_event *event)
>> return new_raw_count;
>> }
>>
>> +static void rapl_start_hrtimer(struct rapl_pmu *pmu)
>> +{
>> + __hrtimer_start_range_ns(&pmu->hrtimer,
>> + pmu->timer_interval, 0,
>> + HRTIMER_MODE_REL_PINNED, 0);
>> +}
>> +
>> +static void rapl_stop_hrtimer(struct rapl_pmu *pmu)
>> +{
>> + hrtimer_cancel(&pmu->hrtimer);
>> +}
>> +
>> +static enum hrtimer_restart rapl_hrtimer_handle(struct hrtimer *hrtimer)
>> +{
>> + struct rapl_pmu *pmu = container_of(hrtimer, struct rapl_pmu, hrtimer);
>> + struct perf_event *event;
>> + unsigned long flags;
>> +
>> + if (!pmu->n_active)
>> + return HRTIMER_NORESTART;
>> +
>> + spin_lock_irqsave(&pmu->lock, flags);
>> +
>> + list_for_each_entry(event, &pmu->active_list, active_entry) {
>> + rapl_event_update(event);
>> + }
>
> hi,
> I dont fully understand the reason for the timer,
> I'm probably missing something..
>
The reason is rather simple and is similar to what happens with uncore.
The counter are narrow, 32-bit and there is no interrupt capability. We
need to poll the counters and accumulate in the sw counter to avoid missing
an overflow.
> - the timer calls rapl_event_update for all defined events
No, only for the defined RAPL events which is what we want.
> - but rapl_pmu_event_read calls rapl_event_update any time the
> event is read (sys_read)
>
Yes, but we want to prevent missing a counter overflow. It may happen
if the counter counts in a unit which increments fast.
> The rapl_event_update only read msr and updates
> event->count|hw,prev_count.
No, it does update the count:
local64_add(sdelta, &event->count);
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