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

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Message-ID: <2339245.XXG4qaq6pt@vostro.rjw.lan>
Date:	Mon, 30 Mar 2015 21:15:34 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	"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 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!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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