Re: [PATCH v3 4/6] cpufreq: powernv: Call throttle_check() on receiving OCC_THROTTLE

Preeti U Murthy
2015-05-07T12:19:35Z

On 05/05/2015 02:11 PM, Preeti U Murthy wrote:
> On 05/05/2015 12:03 PM, Shilpasri G Bhat wrote:
>> Hi Preeti,
>>
>> On 05/05/2015 09:30 AM, Preeti U Murthy wrote:
>>> Hi Shilpa,
>>>
>>> On 05/04/2015 02:24 PM, Shilpasri G Bhat wrote:
>>>> Re-evaluate the chip's throttled state on recieving OCC_THROTTLE
>>>> notification by executing *throttle_check() on any one of the cpu on
>>>> the chip. This is a sanity check to verify if we were indeed
>>>> throttled/unthrottled after receiving OCC_THROTTLE notification.
>>>>
>>>> We cannot call *throttle_check() directly from the notification
>>>> handler because we could be handling chip1's notification in chip2. So
>>>> initiate an smp_call to execute *throttle_check(). We are irq-disabled
>>>> in the notification handler, so use a worker thread to smp_call
>>>> throttle_check() on any of the cpu in the chipmask.
>>>
>>> I see that the first patch takes care of reporting *per-chip* throttling
>>> for pmax capping condition. But where are we taking care of reporting
>>> "pstate set to safe" and "freq control disabled" scenarios per-chip ?
>>>
>>
>> IMO let us not have "psafe" and "freq control disabled" states managed per-chip.
>> Because when the above two conditions occur it is likely to happen across all
>> chips during an OCC reset cycle. So I am setting 'throttled' to false on
>> OCC_ACTIVE and re-verifying if it actually is the case by invoking
>> *throttle_check().
>
> Alright like I pointed in the previous reply, a comment to indicate that
> psafe and freq control disabled conditions will fail when occ is
> inactive and that all chips face the consequence of this will help.

>From your explanation on the thread of the first patch of this series,
this will not be required.

So,
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>

Regards
Preeti U Murthy
>
>>
>>>>
>>>> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
>>>> ---
>>>> drivers/cpufreq/powernv-cpufreq.c | 28 ++++++++++++++++++++++++++--
>>>> 1 file changed, 26 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
>>>> index 9268424..9618813 100644
>>>> --- a/drivers/cpufreq/powernv-cpufreq.c
>>>> +++ b/drivers/cpufreq/powernv-cpufreq.c
>>>> @@ -50,6 +50,8 @@ static bool rebooting, throttled, occ_reset;
>>>> static struct chip {
>>>> unsigned int id;
>>>> bool throttled;
>>>> + cpumask_t mask;
>>>> + struct work_struct throttle;
>>>> } *chips;
>>>>
>>>> static int nr_chips;
>>>> @@ -310,8 +312,9 @@ static inline unsigned int get_nominal_index(void)
>>>> return powernv_pstate_info.max - powernv_pstate_info.nominal;
>>>> }
>>>>
>>>> -static void powernv_cpufreq_throttle_check(unsigned int cpu)
>>>> +static void powernv_cpufreq_throttle_check(void *data)
>>>> {
>>>> + unsigned int cpu = smp_processor_id();
>>>> unsigned long pmsr;
>>>> int pmsr_pmax, pmsr_lp, i;
>>>>
>>>> @@ -373,7 +376,7 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
>>>> return 0;
>>>>
>>>> if (!throttled)
>>>> - powernv_cpufreq_throttle_check(smp_processor_id());
>>>> + powernv_cpufreq_throttle_check(NULL);
>>>>
>>>> freq_data.pstate_id = powernv_freqs[new_index].driver_data;
>>>>
>>>> @@ -418,6 +421,14 @@ static struct notifier_block powernv_cpufreq_reboot_nb = {
>>>> .notifier_call = powernv_cpufreq_reboot_notifier,
>>>> };
>>>>
>>>> +void powernv_cpufreq_work_fn(struct work_struct *work)
>>>> +{
>>>> + struct chip *chip = container_of(work, struct chip, throttle);
>>>> +
>>>> + smp_call_function_any(&chip->mask,
>>>> + powernv_cpufreq_throttle_check, NULL, 0);
>>>> +}
>>>> +
>>>> static char throttle_reason[][30] = {
>>>> "No throttling",
>>>> "Power Cap",
>>>> @@ -433,6 +444,7 @@ static int powernv_cpufreq_occ_msg(struct notifier_block *nb,
>>>> struct opal_msg *occ_msg = msg;
>>>> uint64_t token;
>>>> uint64_t chip_id, reason;
>>>> + int i;
>>>>
>>>> if (msg_type != OPAL_MSG_OCC)
>>>> return 0;
>>>> @@ -466,6 +478,10 @@ static int powernv_cpufreq_occ_msg(struct notifier_block *nb,
>>>> occ_reset = false;
>>>> throttled = false;
>>>> pr_info("OCC: Active\n");
>>>> +
>>>> + for (i = 0; i < nr_chips; i++)
>>>> + schedule_work(&chips[i].throttle);
>>>> +
>>>> return 0;
>>>> }
>>>>
>>>> @@ -476,6 +492,12 @@ static int powernv_cpufreq_occ_msg(struct notifier_block *nb,
>>>> else if (!reason)
>>>> pr_info("OCC: Chip %u %s\n", (unsigned int)chip_id,
>>>> throttle_reason[reason]);
>>>> + else
>>>> + return 0;
>>>
>>> Why the else section ? The code can never reach here, can it ?
>>
>> When reason > 5 , we dont want to handle it.
>
> Of course! My bad!
>>
>>>
>>>> +
>>>> + for (i = 0; i < nr_chips; i++)
>>>> + if (chips[i].id == chip_id)
>>>> + schedule_work(&chips[i].throttle);
>>>> }
>>>
>>> Should we not do this only when we get unthrottled so as to cross verify
>>> if it is indeed the case ? In case of throttling notification, opal's
>>> verdict is final and there is no need to cross verify right ?
>>
>> Two reasons for invoking *throttle_check() on throttling:
>> 1) We just got to know the reason and not the Pmax value we are getting
>> throttled to.
>> 2) It could be a spurious message caused due to late/lost delivery. My point
>> here is let us not completely rely on the notification to declare throttling
>> unless we verify it from reading PMSR.
>
> Sounds good.
>
> Regards
> Preeti U Murthy
>
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