linux-kernel - Re: [PATCH v3] cpufreq: powernv: Report cpu frequency throttling

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Date:	Wed, 01 Apr 2015 15:14:49 +0530
From:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] cpufreq: powernv: Report cpu frequency throttling

Hi Rafael,

On 03/31/2015 12:45 AM, Rafael J. Wysocki wrote:
> On Friday, March 27, 2015 01:10:46 PM Viresh Kumar wrote:
>> On 27 March 2015 at 13:02, Shilpasri G Bhat
>> <shilpa.bhat@...ux.vnet.ibm.com> wrote:
>>> The power and thermal safety of the system is taken care by an
>>> On-Chip-Controller (OCC) which is real-time subsystem embedded within
>>> the POWER8 processor. OCC continuously monitors the memory and core
>>> temperature, the total system power, state of power supply and fan.
>>>
>>> The cpu frequency can be throttled by OCC for the following reasons:
>>> 1)If a processor crosses its power and temperature limit then OCC will
>>>   lower its Pmax to reduce the frequency and voltage.
>>> 2)If OCC crashes then the system is forced to Psafe frequency.
>>> 3)If OCC fails to recover then the kernel is not allowed to do any
>>>   further frequency changes and the chip will remain in Psafe.
>>>
>>> The user can see a drop in performance when frequency is throttled and
>>> is unaware of throttling. So detect and report such a condition so
>>> that user can check the OCC status to reboot the system or check for
>>> power supply or fan failures.
>>>
>>> The current status of the core is read from Power Management Status
>>> Register(PMSR) to check if any of the throttling condition is occurred
>>> and the appropriate throttling message is reported.
>>>
>>> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
>>> ---
>>> Changes from V2:
>>> -Changed commit log to add more details.
>>> -Fixed multi-line comment to proper format
>>>
>>> Changes from V1: Removed unused value of PMCR register
>>>
>>>  drivers/cpufreq/powernv-cpufreq.c | 40 ++++++++++++++++++++++++++++++++++++++-
>>>  1 file changed, 39 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
>>> index 2dfd4fd..0eb89a9 100644
>>> --- a/drivers/cpufreq/powernv-cpufreq.c
>>> +++ b/drivers/cpufreq/powernv-cpufreq.c
>>> @@ -36,7 +36,7 @@
>>>  #define POWERNV_MAX_PSTATES    256
>>>
>>>  static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
>>> -static bool rebooting;
>>> +static bool rebooting, throttled;
>>>
>>>  /*
>>>   * Note: The set of pstates consists of contiguous integers, the
>>> @@ -294,6 +294,41 @@ 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)
>>> +{
>>> +       unsigned long pmsr;
>>> +       int pmsr_pmax, pmsr_lp;
>>> +
>>> +       pmsr = get_pmspr(SPRN_PMSR);
>>> +
>>> +       /* Check for Pmax Capping */
>>> +       pmsr_pmax = (s8)((pmsr >> 32) & 0xFF);
>>> +       if (pmsr_pmax != powernv_pstate_info.max) {
>>> +               throttled = true;
>>> +               pr_warn("Cpu %d Pmax is reduced to %d\n", cpu, pmsr_pmax);
>>> +       }
>>> +
>>> +       /*
>>> +        * Check for Psafe by reading LocalPstate
>>> +        * or check if Psafe_mode_active- 34th bit is set in PMSR.
>>> +        */
>>> +       pmsr_lp = (s8)((pmsr >> 48) & 0xFF);
>>> +       if ((pmsr_lp < powernv_pstate_info.min) || ((pmsr >> 30) & 1)) {
>>> +               throttled = true;
>>> +               pr_warn("Cpu %d in Psafe %d PMSR[34]=%lx\n", cpu,
>>> +                               pmsr_lp, ((pmsr >> 30) & 1));
>>> +       }
>>> +
>>> +       /* Check if SPR_EM_DISABLED- 33rd bit is set in PMSR */
>>> +       if ((pmsr >> 31) & 1) {
>>> +               throttled = true;
>>> +               pr_warn("Frequency management disabled cpu %d PMSR[33]=%lx\n",
>>> +                               cpu, ((pmsr >> 31) & 1));
>>> +       }
>>> +       if (throttled)
>>> +               pr_warn("Cpu Frequency is throttled\n");
>>> +}
>>> +
>>>  /*
>>>   * powernv_cpufreq_target_index: Sets the frequency corresponding to
>>>   * the cpufreq table entry indexed by new_index on the cpus in the
>>> @@ -307,6 +342,9 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
>>>         if (unlikely(rebooting) && new_index != get_nominal_index())
>>>                 return 0;
>>>
>>> +       if (!throttled)
>>> +               powernv_cpufreq_throttle_check(smp_processor_id());
>>> +
>>>         freq_data.pstate_id = powernv_freqs[new_index].driver_data;
>>
>> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 
> Queued up for 4.1, thanks!
> 
> 

Kindly revert this patch. This patch requires additional cosmetic
changes for better readability and maintenance, without any change in
functionality. I would have wanted to post the diff with the additional
changes in this patch but it touches almost the whole thing, so I will
post out v4 version of this patch with all the changes. Apologies for the
inconvenience.

Thanks and Regards,
Shilpa

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