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cpufreq: intel_pstate: Do not use PID-based P-state selection
All systems with a defined ACPI preferred profile that are not "servers" have been using the load-based P-state selection algorithm in intel_pstate since 4.12-rc1 (mobile systems and laptops have been using it since 4.10-rc1) and no problems with it have been reported to date. In particular, no regressions with respect to the PID-based P-state selection have been reported. Also testing indicates that the P-state selection algorithm based on CPU load is generally on par with the PID-based algorithm performance-wise, and for some workloads it turns out to be better than the other one, while being more straightforward and easier to understand at the same time. Moreover, the PID-based P-state selection algorithm in intel_pstate is known to be unstable in some situation and generally problematic, the issues with it are hard to address and it has become a significant maintenance burden. For these reasons, make intel_pstate use the "powersave" P-state selection algorithm based on CPU load in the active mode on all systems and drop the PID-based P-state selection code along with all things related to it from the driver. Also update the documentation accordingly. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Rafael J. Wysocki
parent
520eccdfe1
commit
9d0ef7af1f
@ -167,35 +167,17 @@ is set.
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``powersave``
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.............
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Without HWP, this P-state selection algorithm generally depends on the
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processor model and/or the system profile setting in the ACPI tables and there
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are two variants of it.
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One of them is used with processors from the Atom line and (regardless of the
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processor model) on platforms with the system profile in the ACPI tables set to
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"mobile" (laptops mostly), "tablet", "appliance PC", "desktop", or
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"workstation". It is also used with processors supporting the HWP feature if
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that feature has not been enabled (that is, with the ``intel_pstate=no_hwp``
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argument in the kernel command line). It is similar to the algorithm
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Without HWP, this P-state selection algorithm is similar to the algorithm
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implemented by the generic ``schedutil`` scaling governor except that the
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utilization metric used by it is based on numbers coming from feedback
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registers of the CPU. It generally selects P-states proportional to the
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current CPU utilization, so it is referred to as the "proportional" algorithm.
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current CPU utilization.
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The second variant of the ``powersave`` P-state selection algorithm, used in all
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of the other cases (generally, on processors from the Core line, so it is
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referred to as the "Core" algorithm), is based on the values read from the APERF
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and MPERF feedback registers and the previously requested target P-state.
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It does not really take CPU utilization into account explicitly, but as a rule
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it causes the CPU P-state to ramp up very quickly in response to increased
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utilization which is generally desirable in server environments.
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Regardless of the variant, this algorithm is run by the driver's utilization
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update callback for the given CPU when it is invoked by the CPU scheduler, but
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not more often than every 10 ms (that can be tweaked via ``debugfs`` in `this
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particular case <Tuning Interface in debugfs_>`_). Like in the ``performance``
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case, the hardware configuration is not touched if the new P-state turns out to
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be the same as the current one.
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This algorithm is run by the driver's utilization update callback for the
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given CPU when it is invoked by the CPU scheduler, but not more often than
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every 10 ms. Like in the ``performance`` case, the hardware configuration
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is not touched if the new P-state turns out to be the same as the current
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one.
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This is the default P-state selection algorithm if the
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:c:macro:`CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE` kernel configuration option
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@ -720,34 +702,7 @@ P-state is called, the ``ftrace`` filter can be set to to
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gnome-shell-3409 [001] ..s. 2537.650850: intel_pstate_set_pstate <-intel_pstate_timer_func
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<idle>-0 [000] ..s. 2537.654843: intel_pstate_set_pstate <-intel_pstate_timer_func
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Tuning Interface in ``debugfs``
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-------------------------------
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The ``powersave`` algorithm provided by ``intel_pstate`` for `the Core line of
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processors in the active mode <powersave_>`_ is based on a `PID controller`_
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whose parameters were chosen to address a number of different use cases at the
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same time. However, it still is possible to fine-tune it to a specific workload
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and the ``debugfs`` interface under ``/sys/kernel/debug/pstate_snb/`` is
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provided for this purpose. [Note that the ``pstate_snb`` directory will be
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present only if the specific P-state selection algorithm matching the interface
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in it actually is in use.]
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The following files present in that directory can be used to modify the PID
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controller parameters at run time:
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| ``deadband``
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| ``d_gain_pct``
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| ``i_gain_pct``
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| ``p_gain_pct``
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| ``sample_rate_ms``
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| ``setpoint``
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Note, however, that achieving desirable results this way generally requires
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expert-level understanding of the power vs performance tradeoff, so extra care
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is recommended when attempting to do that.
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.. _LCEU2015: http://events.linuxfoundation.org/sites/events/files/slides/LinuxConEurope_2015.pdf
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.. _SDM: http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-system-programming-manual-325384.html
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.. _ACPI specification: http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf
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.. _PID controller: https://en.wikipedia.org/wiki/PID_controller
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@ -172,28 +172,6 @@ struct vid_data {
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int32_t ratio;
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};
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/**
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* struct _pid - Stores PID data
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* @setpoint: Target set point for busyness or performance
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* @integral: Storage for accumulated error values
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* @p_gain: PID proportional gain
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* @i_gain: PID integral gain
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* @d_gain: PID derivative gain
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* @deadband: PID deadband
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* @last_err: Last error storage for integral part of PID calculation
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*
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* Stores PID coefficients and last error for PID controller.
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*/
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struct _pid {
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int setpoint;
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int32_t integral;
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int32_t p_gain;
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int32_t i_gain;
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int32_t d_gain;
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int deadband;
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int32_t last_err;
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};
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/**
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* struct global_params - Global parameters, mostly tunable via sysfs.
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* @no_turbo: Whether or not to use turbo P-states.
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@ -223,7 +201,6 @@ struct global_params {
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* @last_update: Time of the last update.
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* @pstate: Stores P state limits for this CPU
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* @vid: Stores VID limits for this CPU
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* @pid: Stores PID parameters for this CPU
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* @last_sample_time: Last Sample time
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* @aperf_mperf_shift: Number of clock cycles after aperf, merf is incremented
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* This shift is a multiplier to mperf delta to
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@ -258,7 +235,6 @@ struct cpudata {
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struct pstate_data pstate;
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struct vid_data vid;
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struct _pid pid;
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u64 last_update;
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u64 last_sample_time;
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@ -283,28 +259,6 @@ struct cpudata {
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static struct cpudata **all_cpu_data;
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/**
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* struct pstate_adjust_policy - Stores static PID configuration data
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* @sample_rate_ms: PID calculation sample rate in ms
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* @sample_rate_ns: Sample rate calculation in ns
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* @deadband: PID deadband
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* @setpoint: PID Setpoint
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* @p_gain_pct: PID proportional gain
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* @i_gain_pct: PID integral gain
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* @d_gain_pct: PID derivative gain
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*
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* Stores per CPU model static PID configuration data.
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*/
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struct pstate_adjust_policy {
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int sample_rate_ms;
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s64 sample_rate_ns;
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int deadband;
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int setpoint;
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int p_gain_pct;
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int d_gain_pct;
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int i_gain_pct;
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};
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/**
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* struct pstate_funcs - Per CPU model specific callbacks
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* @get_max: Callback to get maximum non turbo effective P state
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@ -333,15 +287,6 @@ struct pstate_funcs {
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};
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static struct pstate_funcs pstate_funcs __read_mostly;
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static struct pstate_adjust_policy pid_params __read_mostly = {
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.sample_rate_ms = 10,
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.sample_rate_ns = 10 * NSEC_PER_MSEC,
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.deadband = 0,
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.setpoint = 97,
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.p_gain_pct = 20,
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.d_gain_pct = 0,
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.i_gain_pct = 0,
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};
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static int hwp_active __read_mostly;
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static bool per_cpu_limits __read_mostly;
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@ -509,56 +454,6 @@ static inline void intel_pstate_exit_perf_limits(struct cpufreq_policy *policy)
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}
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#endif
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static signed int pid_calc(struct _pid *pid, int32_t busy)
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{
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signed int result;
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int32_t pterm, dterm, fp_error;
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int32_t integral_limit;
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fp_error = pid->setpoint - busy;
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if (abs(fp_error) <= pid->deadband)
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return 0;
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pterm = mul_fp(pid->p_gain, fp_error);
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pid->integral += fp_error;
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/*
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* We limit the integral here so that it will never
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* get higher than 30. This prevents it from becoming
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* too large an input over long periods of time and allows
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* it to get factored out sooner.
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*
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* The value of 30 was chosen through experimentation.
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*/
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integral_limit = int_tofp(30);
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if (pid->integral > integral_limit)
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pid->integral = integral_limit;
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if (pid->integral < -integral_limit)
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pid->integral = -integral_limit;
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dterm = mul_fp(pid->d_gain, fp_error - pid->last_err);
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pid->last_err = fp_error;
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result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm;
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result = result + (1 << (FRAC_BITS-1));
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return (signed int)fp_toint(result);
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}
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static inline void intel_pstate_pid_reset(struct cpudata *cpu)
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{
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struct _pid *pid = &cpu->pid;
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pid->p_gain = percent_fp(pid_params.p_gain_pct);
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pid->d_gain = percent_fp(pid_params.d_gain_pct);
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pid->i_gain = percent_fp(pid_params.i_gain_pct);
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pid->setpoint = int_tofp(pid_params.setpoint);
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pid->last_err = pid->setpoint - int_tofp(100);
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pid->deadband = int_tofp(pid_params.deadband);
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pid->integral = 0;
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}
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static inline void update_turbo_state(void)
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{
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u64 misc_en;
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@ -911,82 +806,6 @@ static void intel_pstate_update_policies(void)
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cpufreq_update_policy(cpu);
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}
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/************************** debugfs begin ************************/
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static int pid_param_set(void *data, u64 val)
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{
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unsigned int cpu;
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*(u32 *)data = val;
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pid_params.sample_rate_ns = pid_params.sample_rate_ms * NSEC_PER_MSEC;
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for_each_possible_cpu(cpu)
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if (all_cpu_data[cpu])
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intel_pstate_pid_reset(all_cpu_data[cpu]);
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return 0;
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}
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static int pid_param_get(void *data, u64 *val)
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{
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*val = *(u32 *)data;
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return 0;
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}
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DEFINE_SIMPLE_ATTRIBUTE(fops_pid_param, pid_param_get, pid_param_set, "%llu\n");
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static struct dentry *debugfs_parent;
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struct pid_param {
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char *name;
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void *value;
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struct dentry *dentry;
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};
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static struct pid_param pid_files[] = {
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{"sample_rate_ms", &pid_params.sample_rate_ms, },
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{"d_gain_pct", &pid_params.d_gain_pct, },
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{"i_gain_pct", &pid_params.i_gain_pct, },
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{"deadband", &pid_params.deadband, },
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{"setpoint", &pid_params.setpoint, },
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{"p_gain_pct", &pid_params.p_gain_pct, },
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{NULL, NULL, }
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};
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static void intel_pstate_debug_expose_params(void)
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{
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int i;
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debugfs_parent = debugfs_create_dir("pstate_snb", NULL);
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if (IS_ERR_OR_NULL(debugfs_parent))
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return;
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for (i = 0; pid_files[i].name; i++) {
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struct dentry *dentry;
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dentry = debugfs_create_file(pid_files[i].name, 0660,
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debugfs_parent, pid_files[i].value,
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&fops_pid_param);
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if (!IS_ERR(dentry))
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pid_files[i].dentry = dentry;
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}
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}
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static void intel_pstate_debug_hide_params(void)
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{
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int i;
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if (IS_ERR_OR_NULL(debugfs_parent))
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return;
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for (i = 0; pid_files[i].name; i++) {
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debugfs_remove(pid_files[i].dentry);
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pid_files[i].dentry = NULL;
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}
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debugfs_remove(debugfs_parent);
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debugfs_parent = NULL;
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}
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/************************** debugfs end ************************/
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/************************** sysfs begin ************************/
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#define show_one(file_name, object) \
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static ssize_t show_##file_name \
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@ -1661,44 +1480,6 @@ static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
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return target;
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}
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static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
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{
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int32_t perf_scaled, max_pstate, current_pstate, sample_ratio;
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u64 duration_ns;
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/*
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* perf_scaled is the ratio of the average P-state during the last
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* sampling period to the P-state requested last time (in percent).
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*
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* That measures the system's response to the previous P-state
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* selection.
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*/
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max_pstate = cpu->pstate.max_pstate_physical;
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current_pstate = cpu->pstate.current_pstate;
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perf_scaled = mul_ext_fp(cpu->sample.core_avg_perf,
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div_fp(100 * max_pstate, current_pstate));
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/*
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* Since our utilization update callback will not run unless we are
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* in C0, check if the actual elapsed time is significantly greater (3x)
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* than our sample interval. If it is, then we were idle for a long
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* enough period of time to adjust our performance metric.
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*/
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duration_ns = cpu->sample.time - cpu->last_sample_time;
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if ((s64)duration_ns > pid_params.sample_rate_ns * 3) {
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sample_ratio = div_fp(pid_params.sample_rate_ns, duration_ns);
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perf_scaled = mul_fp(perf_scaled, sample_ratio);
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} else {
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sample_ratio = div_fp(100 * (cpu->sample.mperf << cpu->aperf_mperf_shift),
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cpu->sample.tsc);
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if (sample_ratio < int_tofp(1))
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perf_scaled = 0;
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}
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cpu->sample.busy_scaled = perf_scaled;
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return cpu->pstate.current_pstate - pid_calc(&cpu->pid, perf_scaled);
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}
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static int intel_pstate_prepare_request(struct cpudata *cpu, int pstate)
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{
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int max_pstate = intel_pstate_get_base_pstate(cpu);
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@ -1741,23 +1522,6 @@ static void intel_pstate_adjust_pstate(struct cpudata *cpu, int target_pstate)
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fp_toint(cpu->iowait_boost * 100));
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}
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static void intel_pstate_update_util_pid(struct update_util_data *data,
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u64 time, unsigned int flags)
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{
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struct cpudata *cpu = container_of(data, struct cpudata, update_util);
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u64 delta_ns = time - cpu->sample.time;
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if ((s64)delta_ns < pid_params.sample_rate_ns)
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return;
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if (intel_pstate_sample(cpu, time)) {
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int target_pstate;
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target_pstate = get_target_pstate_use_performance(cpu);
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intel_pstate_adjust_pstate(cpu, target_pstate);
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}
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}
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static void intel_pstate_update_util(struct update_util_data *data, u64 time,
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unsigned int flags)
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{
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@ -1792,7 +1556,7 @@ static struct pstate_funcs core_funcs = {
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.get_turbo = core_get_turbo_pstate,
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.get_scaling = core_get_scaling,
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.get_val = core_get_val,
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.update_util = intel_pstate_update_util_pid,
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.update_util = intel_pstate_update_util,
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};
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static const struct pstate_funcs silvermont_funcs = {
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@ -1825,7 +1589,7 @@ static const struct pstate_funcs knl_funcs = {
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.get_aperf_mperf_shift = knl_get_aperf_mperf_shift,
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.get_scaling = core_get_scaling,
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.get_val = core_get_val,
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.update_util = intel_pstate_update_util_pid,
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.update_util = intel_pstate_update_util,
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};
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static const struct pstate_funcs bxt_funcs = {
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@ -1879,8 +1643,6 @@ static const struct x86_cpu_id intel_pstate_cpu_ee_disable_ids[] = {
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{}
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};
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static bool pid_in_use(void);
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static int intel_pstate_init_cpu(unsigned int cpunum)
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{
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struct cpudata *cpu;
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@ -1911,8 +1673,6 @@ static int intel_pstate_init_cpu(unsigned int cpunum)
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intel_pstate_disable_ee(cpunum);
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intel_pstate_hwp_enable(cpu);
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} else if (pid_in_use()) {
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intel_pstate_pid_reset(cpu);
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}
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intel_pstate_get_cpu_pstates(cpu);
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@ -2270,12 +2030,6 @@ static struct cpufreq_driver intel_cpufreq = {
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static struct cpufreq_driver *default_driver = &intel_pstate;
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static bool pid_in_use(void)
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{
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return intel_pstate_driver == &intel_pstate &&
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pstate_funcs.update_util == intel_pstate_update_util_pid;
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}
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||||
|
||||
static void intel_pstate_driver_cleanup(void)
|
||||
{
|
||||
unsigned int cpu;
|
||||
@ -2310,9 +2064,6 @@ static int intel_pstate_register_driver(struct cpufreq_driver *driver)
|
||||
|
||||
global.min_perf_pct = min_perf_pct_min();
|
||||
|
||||
if (pid_in_use())
|
||||
intel_pstate_debug_expose_params();
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
@ -2321,9 +2072,6 @@ static int intel_pstate_unregister_driver(void)
|
||||
if (hwp_active)
|
||||
return -EBUSY;
|
||||
|
||||
if (pid_in_use())
|
||||
intel_pstate_debug_hide_params();
|
||||
|
||||
cpufreq_unregister_driver(intel_pstate_driver);
|
||||
intel_pstate_driver_cleanup();
|
||||
|
||||
@ -2391,24 +2139,6 @@ static int __init intel_pstate_msrs_not_valid(void)
|
||||
return 0;
|
||||
}
|
||||
|
||||
#ifdef CONFIG_ACPI
|
||||
static void intel_pstate_use_acpi_profile(void)
|
||||
{
|
||||
switch (acpi_gbl_FADT.preferred_profile) {
|
||||
case PM_MOBILE:
|
||||
case PM_TABLET:
|
||||
case PM_APPLIANCE_PC:
|
||||
case PM_DESKTOP:
|
||||
case PM_WORKSTATION:
|
||||
pstate_funcs.update_util = intel_pstate_update_util;
|
||||
}
|
||||
}
|
||||
#else
|
||||
static void intel_pstate_use_acpi_profile(void)
|
||||
{
|
||||
}
|
||||
#endif
|
||||
|
||||
static void __init copy_cpu_funcs(struct pstate_funcs *funcs)
|
||||
{
|
||||
pstate_funcs.get_max = funcs->get_max;
|
||||
@ -2420,8 +2150,6 @@ static void __init copy_cpu_funcs(struct pstate_funcs *funcs)
|
||||
pstate_funcs.get_vid = funcs->get_vid;
|
||||
pstate_funcs.update_util = funcs->update_util;
|
||||
pstate_funcs.get_aperf_mperf_shift = funcs->get_aperf_mperf_shift;
|
||||
|
||||
intel_pstate_use_acpi_profile();
|
||||
}
|
||||
|
||||
#ifdef CONFIG_ACPI
|
||||
|
||||
Loading…
Reference in New Issue
Block a user