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

From: Preeti U Murthy <[email-masked]>
Date: Tue, 05 May 2015 14:11:48 +0530

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.

> 
>>>
>>> Signed-off-by: Shilpasri G Bhat <[email-masked]>
>>> ---
>>>  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