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

Preeti U Murthy
2015-05-05T08:42:04Z

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 <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