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

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Message-ID: <CAKohponCrbioGcuiPYvB2LjERCBov7E7GApP3HKPwzcC2x1ZYA@mail.gmail.com>
Date:	Fri, 27 Mar 2015 13:10:46 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"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

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>
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