Hi George,
On 6/20/2018 3:17 AM, George Cherian wrote:
> Hi Prakash,
>
> Thanks for the review.
>
> On 06/19/2018 01:51 AM, Prakash, Prashanth wrote:
>> External Email
>>
>> Hi George,
>>
>> On 6/15/2018 4:03 AM, George Cherian wrote:
>>> Per Section 8.4.7.1.3 of ACPI 6.2, The platform provides performance
>>> feedback via set of performance counters. To determine the actual
>>> performance level delivered over time, OSPM may read a set of
>>> performance counters from the Reference Performance Counter Register
>>> and the Delivered Performance Counter Register.
>>>
>>> OSPM calculates the delivered performance over a given time period by
>>> taking a beginning and ending snapshot of both the reference and
>>> delivered performance counters, and calculating:
>>>
>>> delivered_perf = reference_perf X (delta of delivered_perf counter / delta
>>> of reference_perf counter).
>>>
>>> Implement the above and hook this to the cpufreq->get method.
>>>
>>> Signed-off-by: George Cherian <george.cher...@cavium.com>
>>> Acked-by: Viresh Kumar <viresh.ku...@linaro.org>
>>> ---
>>> drivers/cpufreq/cppc_cpufreq.c | 71
>>> ++++++++++++++++++++++++++++++++++++++++++
>>> 1 file changed, 71 insertions(+)
>>>
>>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>>> index 3464580..3fe7625 100644
>>> --- a/drivers/cpufreq/cppc_cpufreq.c
>>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>>> @@ -296,10 +296,81 @@ static int cppc_cpufreq_cpu_init(struct
>>> cpufreq_policy *policy)
>>> return ret;
>>> }
>>>
>>> +static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu,
>>> + struct cppc_perf_fb_ctrs fb_ctrs_t0,
>>> + struct cppc_perf_fb_ctrs fb_ctrs_t1)
>>> +{
>>> + u64 delta_reference, delta_delivered;
>>> + u64 reference_perf, delivered_perf;
>>> +
>>> + reference_perf = fb_ctrs_t0.reference_perf;
>>> + if (fb_ctrs_t1.reference > fb_ctrs_t0.reference) {
>>> + delta_reference = fb_ctrs_t1.reference - fb_ctrs_t0.reference;
>>> + } else {
>> There should be another if () here to check if the reference counters are
>> equal.
>> We cannot assume, there was a overflow when the counters are equal. As I
>> mentioned on last patch, the counters *may* pause in idle states.
> My Bad... I somehow, over looked that point. In case of delta_reference being
> zero there is actually a check below to avoid divide-by-zero. There I
> returned reference perf instead of desired perf, same I will take care in
> v3. Isn't that sufficient or is there a need for an explicit check here for
> delta = zero?
I am not sure I followed the above. The gist of my comment was when the counters
are equal we cannot assume that there was a overflow. So change the ">"
condition
to ">=" and my concern about assuming overflow when equal should be take care
of.
The above change would be required for both reference and delivered counters.
