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 <[email protected]>
Acked-by: Viresh Kumar <[email protected]>
---
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 {
+ /*
+ * Counters would have wrapped-around
+ * We also need to find whether the low level fw
+ * maintains 32 bit or 64 bit counters, to calculate
+ * the correct delta.
+ */
+ if (fb_ctrs_t0.reference > (~(u32)0))
+ delta_reference = (~((u64)0) - fb_ctrs_t0.reference) +
+ fb_ctrs_t1.reference;
+ else
+ delta_reference = (~((u32)0) - fb_ctrs_t0.reference) +
+ fb_ctrs_t1.reference;
+ }
+
+ if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered) {
+ delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered;
+ } else {
+ /*
+ * Counters would have wrapped-around
+ * We also need to find whether the low level fw
+ * maintains 32 bit or 64 bit counters, to calculate
+ * the correct delta.
+ */
+ if (fb_ctrs_t0.delivered > (~(u32)0))
+ delta_delivered = (~((u64)0) - fb_ctrs_t0.delivered) +
+ fb_ctrs_t1.delivered;
+ else
+ delta_delivered = (~((u32)0) - fb_ctrs_t0.delivered) +
+ fb_ctrs_t1.delivered;
+ }
+
+ if (delta_reference) /* Check to avoid divide-by zero */
+ delivered_perf = (reference_perf * delta_delivered) /
+ delta_reference;
+ else
+ delivered_perf = reference_perf;
+
+ return cppc_cpufreq_perf_to_khz(cpu, delivered_perf);
+}
+
+static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
+{
+ struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
+ struct cppc_cpudata *cpu = all_cpu_data[cpunum];
+ int ret;
+
+ ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
+ if (ret)
+ return ret;
+
+ udelay(2); /* 2usec delay between sampling */
+
+ ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1);
+ if (ret)
+ return ret;
+
+ return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1);
+}
+
static struct cpufreq_driver cppc_cpufreq_driver = {
.flags = CPUFREQ_CONST_LOOPS,
.verify = cppc_verify_policy,
.target = cppc_cpufreq_set_target,
+ .get = cppc_cpufreq_get_rate,
.init = cppc_cpufreq_cpu_init,
.stop_cpu = cppc_cpufreq_stop_cpu,
.name = "cppc_cpufreq",
--
2.7.4
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 <[email protected]>
> Acked-by: Viresh Kumar <[email protected]>
> ---
> 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.
> + /*
> + * Counters would have wrapped-around
> + * We also need to find whether the low level fw
> + * maintains 32 bit or 64 bit counters, to calculate
> + * the correct delta.
> + */
> + if (fb_ctrs_t0.reference > (~(u32)0))
> + delta_reference = (~((u64)0) - fb_ctrs_t0.reference) +
> + fb_ctrs_t1.reference;
> + else
> + delta_reference = (~((u32)0) - fb_ctrs_t0.reference) +
> + fb_ctrs_t1.reference;
> + }
> +
> + if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered) {
> + delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered;
> + } else {
> + /*
> + * Counters would have wrapped-around
> + * We also need to find whether the low level fw
> + * maintains 32 bit or 64 bit counters, to calculate
> + * the correct delta.
> + */
> + if (fb_ctrs_t0.delivered > (~(u32)0))
> + delta_delivered = (~((u64)0) - fb_ctrs_t0.delivered) +
> + fb_ctrs_t1.delivered;
> + else
> + delta_delivered = (~((u32)0) - fb_ctrs_t0.delivered) +
> + fb_ctrs_t1.delivered;
> + }
> +
> + if (delta_reference) /* Check to avoid divide-by zero */
> + delivered_perf = (reference_perf * delta_delivered) /
> + delta_reference;
> + else
> + delivered_perf = reference_perf;
If we cannot compute delivered performance then we should return
desired/requested perf and not reference_perf.
> +
> + return cppc_cpufreq_perf_to_khz(cpu, delivered_perf);
> +}
> +
> +static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
> +{
> + struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
> + struct cppc_cpudata *cpu = all_cpu_data[cpunum];
> + int ret;
> +
> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
> + if (ret)
> + return ret;
> +
> + udelay(2); /* 2usec delay between sampling */
> +
> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1);
> + if (ret)
> + return ret;
> +
> + return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1);
> +}
> +
> static struct cpufreq_driver cppc_cpufreq_driver = {
> .flags = CPUFREQ_CONST_LOOPS,
> .verify = cppc_verify_policy,
> .target = cppc_cpufreq_set_target,
> + .get = cppc_cpufreq_get_rate,
> .init = cppc_cpufreq_cpu_init,
> .stop_cpu = cppc_cpufreq_stop_cpu,
> .name = "cppc_cpufreq",
Thanks,
Prashanth
Hi George,
Few comments on your patch:
On Fri, Jun 15, 2018 at 03:03:15AM -0700, 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 <[email protected]>
> Acked-by: Viresh Kumar <[email protected]>
> ---
> 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 {
> + /*
> + * Counters would have wrapped-around
> + * We also need to find whether the low level fw
> + * maintains 32 bit or 64 bit counters, to calculate
> + * the correct delta.
> + */
> + if (fb_ctrs_t0.reference > (~(u32)0))
> + delta_reference = (~((u64)0) - fb_ctrs_t0.reference) +
> + fb_ctrs_t1.reference;
> + else
> + delta_reference = (~((u32)0) - fb_ctrs_t0.reference) +
> + fb_ctrs_t1.reference;
> + }
> +
> + if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered) {
> + delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered;
> + } else {
> + /*
> + * Counters would have wrapped-around
> + * We also need to find whether the low level fw
> + * maintains 32 bit or 64 bit counters, to calculate
> + * the correct delta.
> + */
> + if (fb_ctrs_t0.delivered > (~(u32)0))
> + delta_delivered = (~((u64)0) - fb_ctrs_t0.delivered) +
> + fb_ctrs_t1.delivered;
> + else
> + delta_delivered = (~((u32)0) - fb_ctrs_t0.delivered) +
> + fb_ctrs_t1.delivered;
> + }
Having this code repeated twice does not look great. Also the math here
is not correct, since (~0 - val2 + val1) is off by one. Because of
binary representation, unsigned subtraction will work even if
val2 < val1. So cleaner way would be to do:
static inline u64 ts_sub(u64 t1, u64 t0)
{
if (t1 > t0 || t0 > ~(u32)0)
return t1 - t0;
return (u32)t1 - (u32)t0;
}
And then use ts_sub in both places above.
JC.
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 <[email protected]>
>> Acked-by: Viresh Kumar <[email protected]>
>> ---
>> 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?
Moreover the delta calculation am planning to replace with single
line comparison in v3 for both normal and overflow case.
>> + /*
>> + * Counters would have wrapped-around
>> + * We also need to find whether the low level fw
>> + * maintains 32 bit or 64 bit counters, to calculate
>> + * the correct delta.
>> + */
>> + if (fb_ctrs_t0.reference > (~(u32)0))
>> + delta_reference = (~((u64)0) - fb_ctrs_t0.reference) +
>> + fb_ctrs_t1.reference;
>> + else
>> + delta_reference = (~((u32)0) - fb_ctrs_t0.reference) +
>> + fb_ctrs_t1.reference;
>> + }
>> +
>> + if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered) {
>> + delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered;
>> + } else {
>> + /*
>> + * Counters would have wrapped-around
>> + * We also need to find whether the low level fw
>> + * maintains 32 bit or 64 bit counters, to calculate
>> + * the correct delta.
>> + */
>> + if (fb_ctrs_t0.delivered > (~(u32)0))
>> + delta_delivered = (~((u64)0) - fb_ctrs_t0.delivered) +
>> + fb_ctrs_t1.delivered;
>> + else
>> + delta_delivered = (~((u32)0) - fb_ctrs_t0.delivered) +
>> + fb_ctrs_t1.delivered;
>> + }
>> +
>> + if (delta_reference) /* Check to avoid divide-by zero */
>> + delivered_perf = (reference_perf * delta_delivered) /
>> + delta_reference;
>> + else
>> + delivered_perf = reference_perf;
>
> If we cannot compute delivered performance then we should return
> desired/requested perf and not reference_perf.
>
Noted!!
>> +
>> + return cppc_cpufreq_perf_to_khz(cpu, delivered_perf);
>> +}
>> +
>> +static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
>> +{
>> + struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>> + struct cppc_cpudata *cpu = all_cpu_data[cpunum];
>> + int ret;
>> +
>> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
>> + if (ret)
>> + return ret;
>> +
>> + udelay(2); /* 2usec delay between sampling */
>> +
>> + ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1);
>> + if (ret)
>> + return ret;
>> +
>> + return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1);
>> +}
>> +
>> static struct cpufreq_driver cppc_cpufreq_driver = {
>> .flags = CPUFREQ_CONST_LOOPS,
>> .verify = cppc_verify_policy,
>> .target = cppc_cpufreq_set_target,
>> + .get = cppc_cpufreq_get_rate,
>> .init = cppc_cpufreq_cpu_init,
>> .stop_cpu = cppc_cpufreq_stop_cpu,
>> .name = "cppc_cpufreq",
>
> Thanks,
> Prashanth
>
Thanks,
-George
Hi JC,
Thanks for the review.
On 06/20/2018 02:09 AM, Jayachandran C wrote:
> Hi George,
>
> Few comments on your patch:
>
> On Fri, Jun 15, 2018 at 03:03:15AM -0700, 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 <[email protected]>
>> Acked-by: Viresh Kumar <[email protected]>
>> ---
>> 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 {
>> + /*
>> + * Counters would have wrapped-around
>> + * We also need to find whether the low level fw
>> + * maintains 32 bit or 64 bit counters, to calculate
>> + * the correct delta.
>> + */
>> + if (fb_ctrs_t0.reference > (~(u32)0))
>> + delta_reference = (~((u64)0) - fb_ctrs_t0.reference) +
>> + fb_ctrs_t1.reference;
>> + else
>> + delta_reference = (~((u32)0) - fb_ctrs_t0.reference) +
>> + fb_ctrs_t1.reference;
>> + }
>> +
>> + if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered) {
>> + delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered;
>> + } else {
>> + /*
>> + * Counters would have wrapped-around
>> + * We also need to find whether the low level fw
>> + * maintains 32 bit or 64 bit counters, to calculate
>> + * the correct delta.
>> + */
>> + if (fb_ctrs_t0.delivered > (~(u32)0))
>> + delta_delivered = (~((u64)0) - fb_ctrs_t0.delivered) +
>> + fb_ctrs_t1.delivered;
>> + else
>> + delta_delivered = (~((u32)0) - fb_ctrs_t0.delivered) +
>> + fb_ctrs_t1.delivered;
>> + }
>
> Having this code repeated twice does not look great. Also the math here
> is not correct, since (~0 - val2 + val1) is off by one. Because of
> binary representation, unsigned subtraction will work even if
> val2 < val1. So cleaner way would be to do:
>
> static inline u64 ts_sub(u64 t1, u64 t0)
> {
> if (t1 > t0 || t0 > ~(u32)0)
> return t1 - t0;
>
> return (u32)t1 - (u32)t0;
> }
>
> And then use ts_sub in both places above.
I was actually thinking to replace the whole comparison with a single
line irrespective of rollover or not.
It will look something like this.
delta = (u32)(((1UL << 32) - t0) + t1);
This will also take care of the value being off by one.
>
> JC.
>
Regards,
-George
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 <[email protected]>
>>> Acked-by: Viresh Kumar <[email protected]>
>>> ---
>>> 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.