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

From: Shilpasri G Bhat <[email-masked]>
Date: Tue, 05 May 2015 12:03:00 +0530

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().

>>
>> 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.

> 
>> +
>> +		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.

> 
> Perhaps the one thing that needs to be taken care in addition to
> reporting throttling is setting the chip's throttled parameter to true.
> This should do right ? I don't see the need to call throttle_check() here.
> 
>

Thanks and Regards,
Shilpa