Re: [Xen-devel] [RFC PATCH 04/31] cpufreq: make turbo settings to be configurable

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

....

> And the most important question is how to recognize in Xen on ARM
> (using SCPI protocol) which frequencies are turbo-frequencies
> actually? I couldn't find any information regarding that in protocol
> description.

So traditionally on ARM there is no notion of a "turbo" frequency. The
idea is to expose the highest possible frequency, and let thermal
throttling (possibly in hardware or in firmware) limit the frequency if
the thermal budget is busted.
Also in the ARM world it is expected that an OS has much better
knowledge on how to handle frequencies, for instance when to give more
power to the GPU and when to the CPU.

> For DT-based CPUFreq it is not an issue, since there is a specific
> property "turbo-mode" to mark corresponding OPPs. [1].
> But neither SCPI DT bindings [2] nor the SCPI protocol itself [3]
> mentions about it. Perhaps, additional command should be added to pass
> such info.

The DT binding you mentioned in Linux is a generic one.
In general DT only describes non-discoverable properties. But for SCPI
the OPPs are handled in the SCP and advertised via SCPI calls (3.2.9 Get
DVFS Info, command 0x9).
So the OPP table is not in the DT, and thus you don't have any way of
detecting turbo frequencies.
But as mentioned before, this is so by design, as ARM does not endorse
the concept of turbo frequencies in general.

Now with the advent of more "server-y" chips and ACPI, this might change
in the future. For instance SCMI is designed to be closer to ACPI, so we
might inherit some turbo notion from there.

So we should not completely rule out the idea of turbo, but for a start
we can somewhat assume that an ARM based system does not have turbo per se.

Cheers,
Andre.

> [1] https://www.kernel.org/doc/Documentation/devicetree/bindings/opp/opp.txt
> [2] 
> http://elixir.free-electrons.com/linux/v4.15-rc1/source/Documentation/devicetree/bindings/arm/arm,scpi.txt
> [3] 
> http://infocenter.arm.com/help/topic/com.arm.doc.dui0922g/scp_message_interface_v1_2_DUI0922G_en.pdf
> 
>>
>>
>>> diff --git a/xen/drivers/pm/stat.c b/xen/drivers/pm/stat.c
>>> index 2dbde1c..133e64d 100644
>>> --- a/xen/drivers/pm/stat.c
>>> +++ b/xen/drivers/pm/stat.c
>>> @@ -290,7 +290,11 @@ static int get_cpufreq_para(struct xen_sysctl_pm_op 
>>> *op)
>>>              &op->u.get_para.u.ondemand.sampling_rate,
>>>              &op->u.get_para.u.ondemand.up_threshold);
>>>      }
>>> +#ifdef CONFIG_HAS_CPU_TURBO
>>>      op->u.get_para.turbo_enabled = cpufreq_get_turbo_status(op->cpuid);
>>> +#else
>>> +    op->u.get_para.turbo_enabled = 0;
>>> +#endif
>>>
>>>      return ret;
>>>  }
>>> @@ -473,6 +477,7 @@ int do_pm_op(struct xen_sysctl_pm_op *op)
>>>          break;
>>>      }
>>>
>>> +#ifdef CONFIG_HAS_CPU_TURBO
>>>      case XEN_SYSCTL_pm_op_enable_turbo:
>>>      {
>>>          ret = cpufreq_update_turbo(op->cpuid, CPUFREQ_TURBO_ENABLED);
>>> @@ -484,6 +489,7 @@ int do_pm_op(struct xen_sysctl_pm_op *op)
>>>          ret = cpufreq_update_turbo(op->cpuid, CPUFREQ_TURBO_DISABLED);
>>>          break;
>>>      }
>>> +#endif /* CONFIG_HAS_CPU_TURBO */
>>>
>>>      default:
>>>          printk("not defined sub-hypercall @ do_pm_op\n");
>>> diff --git a/xen/include/xen/cpufreq.h b/xen/include/xen/cpufreq.h
>>> index 30c70c9..2e0c16a 100644
>>> --- a/xen/include/xen/cpufreq.h
>>> +++ b/xen/include/xen/cpufreq.h
>>> @@ -39,7 +39,9 @@ extern struct acpi_cpufreq_data 
>>> *cpufreq_drv_data[NR_CPUS];
>>>
>>>  struct cpufreq_cpuinfo {
>>>      unsigned int        max_freq;
>>> +#ifdef CONFIG_HAS_CPU_TURBO
>>>      unsigned int        second_max_freq;    /* P1 if Turbo Mode is on */
>>> +#endif
>>>      unsigned int        min_freq;
>>>      unsigned int        transition_latency; /* in 10^(-9) s = nanoseconds 
>>> */
>>>  };
>>> @@ -72,9 +74,11 @@ struct cpufreq_policy {
>>>
>>>      bool_t              resume; /* flag for cpufreq 1st run
>>>                                   * S3 wakeup, hotplug cpu, etc */
>>> +#ifdef CONFIG_HAS_CPU_TURBO
>>>      s8                  turbo;  /* tristate flag: 0 for unsupported
>>>                                   * -1 for disable, 1 for enabled
>>>                                   * See CPUFREQ_TURBO_* below for defines */
>>> +#endif
>>>      bool_t              aperf_mperf; /* CPU has APERF/MPERF MSRs */
>>>  };
>>>  DECLARE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_policy);
>>> @@ -138,8 +142,10 @@ extern int cpufreq_driver_getavg(unsigned int cpu, 
>>> unsigned int flag);
>>>  #define CPUFREQ_TURBO_UNSUPPORTED   0
>>>  #define CPUFREQ_TURBO_ENABLED       1
>>>
>>> +#ifdef CONFIG_HAS_CPU_TURBO
>>>  extern int cpufreq_update_turbo(int cpuid, int new_state);
>>>  extern int cpufreq_get_turbo_status(int cpuid);
>>> +#endif
>>>
>>>  static __inline__ int
>>>  __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event)
> 
> 
> 

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