linux-kernel - Re: [RESEND PATCH V2 1/4] perf/x86/intel: fix event update for auto-reload

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Date:   Wed, 10 Jan 2018 09:31:01 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     kan.liang@...el.com, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        eranian@...gle.com, ak@...ux.intel.com
Subject: Re: [RESEND PATCH V2 1/4] perf/x86/intel: fix event update for
 auto-reload



On 1/10/2018 5:22 AM, Jiri Olsa wrote:
> On Mon, Jan 08, 2018 at 07:15:13AM -0800, kan.liang@...el.com wrote:
> 
> SNIP
> 
>> There is nothing need to do in x86_perf_event_set_period(). Because it
>> is fixed period. The period_left is already adjusted.
>>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>>   arch/x86/events/intel/ds.c | 69 ++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 67 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
>> index 3674a4b..cc1f373 100644
>> --- a/arch/x86/events/intel/ds.c
>> +++ b/arch/x86/events/intel/ds.c
>> @@ -1251,17 +1251,82 @@ get_next_pebs_record_by_bit(void *base, void *top, int bit)
>>   	return NULL;
>>   }
>>   
>> +/*
>> + * Specific intel_pmu_save_and_restart() for auto-reload.
>> + */
>> +static int intel_pmu_save_and_restart_reload(struct perf_event *event,
>> +					     u64 reload_val,
>> +					     int reload_times)
>> +{
>> +	struct hw_perf_event *hwc = &event->hw;
>> +	int shift = 64 - x86_pmu.cntval_bits;
>> +	u64 prev_raw_count, new_raw_count;
>> +	u64 delta;
>> +
>> +	if ((reload_times == 0) || (reload_val == 0))
>> +		return intel_pmu_save_and_restart(event);
> 
> why is this check needed? AFAICS __intel_pmu_pebs_event is
> called only if reload_times != 0 and reload_val is always
> non zero for sampling
> 

Here is a sanity check for reload_times and reload_val.
Right, usually they are non zero.
I think it should not bring any issues. Right?
If so, I think we may still keep it?

Thanks,
Kan