cpufreq: intel_pstate: Enforce _PPC limits

Use ACPI _PPC notification to limit max P state driver will request.
ACPI _PPC change notification is sent by BIOS to limit max P state
in several cases:
-

cpufreq: intel_pstate: Enforce _PPC limits

Use ACPI _PPC notification to limit max P state driver will request.
ACPI _PPC change notification is sent by BIOS to limit max P state
in several cases:
- Reduce impact of platform thermal condition
- When Config TDP feature is used, a changed _PPC is sent to
follow TDP change
- Remote node managers in server want to control platform power
via baseboard management controller (BMC)

This change registers with ACPI processor performance lib so that
_PPC changes are notified to cpufreq core, which in turns will
result in call to .setpolicy() callback. Also the way _PSS
table identifies a turbo frequency is not compatible to max turbo
frequency in intel_pstate, so the very first entry in _PSS needs
to be adjusted.

This feature can be turned on by using kernel parameters:
intel_pstate=support_acpi_ppc

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[ rjw: Minor cleanups ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Fix processing for turbo activation ratio

When the config TDP level is not nominal (level = 0), the MSR values for
reading level 1 and level 2 ratios contain power in low 14 b

cpufreq: intel_pstate: Fix processing for turbo activation ratio

When the config TDP level is not nominal (level = 0), the MSR values for
reading level 1 and level 2 ratios contain power in low 14 bits and actual
ratio bits are at bits [23:16]. The current processing for level 1 and
level 2 is wrong as there is no shift done to get actual ratio.

Fixes: 6a35fc2d6c22 (cpufreq: intel_pstate: get P1 from TAR when available)
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: 4.4+ <stable@vger.kernel.org> # 4.4+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Use average P-State instead of current P-State

The result returned by pid_calc() is subtracted from current_pstate
(which is the P-State requested during the last period) in o

cpufreq: intel_pstate: Use average P-State instead of current P-State

The result returned by pid_calc() is subtracted from current_pstate
(which is the P-State requested during the last period) in order to
obtain the target P-State for the current iteration.

However, current_pstate may not reflect the real current P-State of
the CPU. In particular, that P-State may be higher because of the
frequency sharing per module.

The theory is:
- The load is the percentage of time spent in C0 and is related to
the average P-State during the same period.
- The last requested P-State can be completely different than the
average P-State (because of frequency sharing or throttling).
- The P-State shift computed by the pid_calc is based on the load
computed at average P-State, so the shift must be relative to
this average P-State.

Using the average P-State instead of current P-State improves power
without significant performance penalty in cases when a task migrates
from one core to other core sharing frequency and voltage.

Performance and power comparison with this patch on Cherry Trail
platform using Android:

Benchmark ?Perf ?Power
FishTank 10.45% 3.1%
SmartBench-Gaming -0.1% -10.4%
SmartBench-Productivity -0.8% -10.4%
CandyCrush n/a -17.4%
AngryBirds n/a -5.9%
videoPlayback n/a -13.9%
audioPlayback n/a -4.9%
IcyRocks-20-50 0.0% -38.4%
iozone RR -0.16% -1.3%
iozone RW 0.74% -1.3%

Signed-off-by: Philippe Longepe <philippe.longepe@linux.intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Avoid getting stuck in high P-states when idle

Jörg Otte reports that commit a4675fbc4a7a (cpufreq: intel_pstate:
Replace timers with utilization update callbacks) caused the CPUs in
h

intel_pstate: Avoid getting stuck in high P-states when idle

Jörg Otte reports that commit a4675fbc4a7a (cpufreq: intel_pstate:
Replace timers with utilization update callbacks) caused the CPUs in
his Haswell-based system to stay in the very high frequency region
even if the system is completely idle.

That turns out to be an existing problem in the intel_pstate driver's
P-state selection algorithm for Core processors. Namely, all
decisions made by that algorithm are based on the average frequency
of the CPU between sampling events and on the P-state requested on
the last invocation, so it may get stuck at a very hight frequency
even if the utilization of the CPU is very low (in fact, it may get
stuck in a inadequate P-state regardless of the CPU utilization).
The only way to kick it out of that limbo is a sufficiently long idle
period (3 times longer than the prescribed sampling interval), but if
that doesn't happen often enough (eg. due to a timing change like
after the above commit), the P-state of the CPU may be inadequate
pretty much all the time.

To address the most egregious manifestations of that issue, reset the
core_busy value used to determine the next P-state to request if the
utilization of the CPU, determined with the help of the MPERF
feedback register and the TSC, is below 1%.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=115771
Reported-and-tested-by: Jörg Otte <jrg.otte@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Use pr_fmt

Prefix the output using the more common kernel style.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked

intel_pstate: Use pr_fmt

Prefix the output using the more common kernel style.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
[ rjw: Rebase ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Avoid pointless FRAC_BITS shifts under div_fp()

There are multiple places in intel_pstate where int_tofp() is applied
to both arguments of div_fp(), but this is pointless, because int_

intel_pstate: Avoid pointless FRAC_BITS shifts under div_fp()

There are multiple places in intel_pstate where int_tofp() is applied
to both arguments of div_fp(), but this is pointless, because int_tofp()
simply shifts its argument to the left by FRAC_BITS which mathematically
is equivalent to multuplication by 2^FRAC_BITS, so if this is done
to both arguments of a division, the extra factors will cancel each
other during that operation anyway.

Drop the pointless int_tofp() applied to div_fp() arguments throughout
the driver.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Documenation for structures

No code change. Only added kernel doc style comments for structures.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Sign

cpufreq: intel_pstate: Documenation for structures

No code change. Only added kernel doc style comments for structures.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: fix inconsistency in setting policy limits

When user sets performance policy using cpufreq interface, it is possible
that because of policy->max limits, the actual performance

cpufreq: intel_pstate: fix inconsistency in setting policy limits

When user sets performance policy using cpufreq interface, it is possible
that because of policy->max limits, the actual performance is still
limited. But the current implementation will silently switch the
policy to powersave and start using powersave limits. If user modifies
any limits using intel_pstate sysfs, this is actually changing powersave
limits.

The current implementation tracks limits under powersave and performance
policy using two different variables. When policy->max is less than
policy->cpuinfo.max_freq, only powersave limit variable is used.

This fix causes the performance limits variable to be used always when
the policy is performance.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: sched: Helpers to add and remove update_util hooks

Replace the single helper for adding and removing cpufreq utilization
update hooks, cpufreq_set_update_util_data(), with a pair of helpers

cpufreq: sched: Helpers to add and remove update_util hooks

Replace the single helper for adding and removing cpufreq utilization
update hooks, cpufreq_set_update_util_data(), with a pair of helpers,
cpufreq_add_update_util_hook() and cpufreq_remove_update_util_hook(),
and modify the users of cpufreq_set_update_util_data() accordingly.

With the new helpers, the code using them doesn't need to worry
about the internals of struct update_util_data and in particular
it doesn't need to worry about populating the func field in it
properly upfront.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

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intel_pstate: Avoid extra invocation of intel_pstate_sample()

The initialization of intel_pstate for a given CPU involves populating
the fields of its struct cpudata that represent the previous samp

intel_pstate: Avoid extra invocation of intel_pstate_sample()

The initialization of intel_pstate for a given CPU involves populating
the fields of its struct cpudata that represent the previous sample,
but currently that is done in a problematic way.

Namely, intel_pstate_init_cpu() makes an extra call to
intel_pstate_sample() so it reads the current register values that
will be used to populate the "previous sample" record during the
next invocation of intel_pstate_sample(). However, after commit
a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with utilization
update callbacks) that doesn't work for last_sample_time, because
the time value is passed to intel_pstate_sample() as an argument now.
Passing 0 to it from intel_pstate_init_cpu() is problematic, because
that causes cpu->last_sample_time == 0 to be visible in
get_target_pstate_use_performance() (and hence the extra
cpu->last_sample_time > 0 check in there) and effectively allows
the first invocation of intel_pstate_sample() from
intel_pstate_update_util() to happen immediately after the
initialization which may lead to a significant "turn on"
effect in the governor algorithm.

To mitigate that issue, rework the initialization to avoid the
extra intel_pstate_sample() call from intel_pstate_init_cpu().
Instead, make intel_pstate_sample() return false if it has been
called with cpu->sample.time equal to zero, which will make
intel_pstate_update_util() skip the sample in that case, and
reset cpu->sample.time from intel_pstate_set_update_util_hook()
to make the algorithm start properly every time the hook is set.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Do not set utilization update hook too early

The utilization update hook in the intel_pstate driver is set too
early, as it only should be set after the policy has been fully
initializ

intel_pstate: Do not set utilization update hook too early

The utilization update hook in the intel_pstate driver is set too
early, as it only should be set after the policy has been fully
initialized by the core. That may cause intel_pstate_update_util()
to use incorrect data and put the CPUs into incorrect P-states as
a result.

To prevent that from happening, make intel_pstate_set_policy() set
the utilization update hook instead of intel_pstate_init_cpu() so
intel_pstate_update_util() only runs when all things have been
initialized as appropriate.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Do not call wrmsrl_on_cpu() with disabled interrupts

After commit a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with
utilization update callbacks) wrmsrl_on_cpu() cannot be calle

intel_pstate: Do not call wrmsrl_on_cpu() with disabled interrupts

After commit a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with
utilization update callbacks) wrmsrl_on_cpu() cannot be called in the
intel_pstate_adjust_busy_pstate() path as that is executed with
disabled interrupts. However, atom_set_pstate() called from there
via intel_pstate_set_pstate() uses wrmsrl_on_cpu() to update the
IA32_PERF_CTL MSR which triggers the WARN_ON_ONCE() in
smp_call_function_single().

The reason why wrmsrl_on_cpu() is used by atom_set_pstate() is
because intel_pstate_set_pstate() calling it is also invoked during
the initialization and cleanup of the driver and in those cases it is
not guaranteed to be run on the CPU that is being updated. However,
in the case when intel_pstate_set_pstate() is called by
intel_pstate_adjust_busy_pstate(), wrmsrl() can be used to update
the register safely. Moreover, intel_pstate_set_pstate() already
contains code that only is executed if the function is called by
intel_pstate_adjust_busy_pstate() and there is a special argument
passed to it because of that.

To fix the problem at hand, rearrange the code taking the above
observations into account.

First, replace the ->set() callback in struct pstate_funcs with a
->get_val() one that will return the value to be written to the
IA32_PERF_CTL MSR without updating the register.

Second, split intel_pstate_set_pstate() into two functions,
intel_pstate_update_pstate() to be called by
intel_pstate_adjust_busy_pstate() that will contain all of the
intel_pstate_set_pstate() code which only needs to be executed in
that case and will use wrmsrl() to update the MSR (after obtaining
the value to write to it from the ->get_val() callback), and
intel_pstate_set_min_pstate() to be invoked during the
initialization and cleanup that will set the P-state to the
minimum one and will update the MSR using wrmsrl_on_cpu().

Finally, move the code shared between intel_pstate_update_pstate()
and intel_pstate_set_min_pstate() to a new static inline function
intel_pstate_record_pstate() and make them both call it.

Of course, that unifies the handling of the IA32_PERF_CTL MSR writes
between Atom and Core.

Fixes: a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with utilization update callbacks)
Reported-and-tested-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Do not skip samples partially

If the current value of MPERF or the current value of TSC is the
same as the previous one, respectively, intel_pstate_sample() bails
out early and skips t

intel_pstate: Do not skip samples partially

If the current value of MPERF or the current value of TSC is the
same as the previous one, respectively, intel_pstate_sample() bails
out early and skips the sample.

However, intel_pstate_adjust_busy_pstate() is still called in that
case which is not correct, so modify intel_pstate_sample() to
return a bool value indicating whether or not the sample has been
taken and use it to decide whether or not to call
intel_pstate_adjust_busy_pstate().

While at it, remove redundant parentheses from the MPERF/TSC
check in intel_pstate_sample().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

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intel_pstate: Remove freq calculation from intel_pstate_calc_busy()

Use a helper function to compute the average pstate and call it only
where it is needed (only when tracing or in intel_pstate_get)

intel_pstate: Remove freq calculation from intel_pstate_calc_busy()

Use a helper function to compute the average pstate and call it only
where it is needed (only when tracing or in intel_pstate_get).

Signed-off-by: Philippe Longepe <philippe.longepe@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()

The cpu_load algorithm doesn't need to invoke intel_pstate_calc_busy(),
so move that call from intel_pstate_sampl

intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()

The cpu_load algorithm doesn't need to invoke intel_pstate_calc_busy(),
so move that call from intel_pstate_sample() to
get_target_pstate_use_performance().

Signed-off-by: Philippe Longepe <philippe.longepe@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Optimize calculation for max/min_perf_adj

mul_fp(int_tofp(A), B) expands to:
((A << FRAC_BITS) * B) >> FRAC_BITS, so the same result can be obtained
via simple multiplication A * B. A

intel_pstate: Optimize calculation for max/min_perf_adj

mul_fp(int_tofp(A), B) expands to:
((A << FRAC_BITS) * B) >> FRAC_BITS, so the same result can be obtained
via simple multiplication A * B. Apply this observation to
max_perf * limits->max_perf and max_perf * limits->min_perf in
intel_pstate_get_min_max()."

Signed-off-by: Philippe Longepe <philippe.longepe@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Remove extra conversions in pid calculation

pid->setpoint and pid->deadband can be initialized in fixed point, so we
can avoid the int_tofp in pid_calc.

Signed-off-by: Philippe Longep

intel_pstate: Remove extra conversions in pid calculation

pid->setpoint and pid->deadband can be initialized in fixed point, so we
can avoid the int_tofp in pid_calc.

Signed-off-by: Philippe Longepe <philippe.longepe@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: Reduce cpufreq_update_util() overhead a bit

Use the observation that cpufreq_update_util() is only called
by the scheduler with rq->lock held, so the callers of
cpufreq_set_update_util_data

cpufreq: Reduce cpufreq_update_util() overhead a bit

Use the observation that cpufreq_update_util() is only called
by the scheduler with rq->lock held, so the callers of
cpufreq_set_update_util_data() can use synchronize_sched()
instead of synchronize_rcu() to wait for cpufreq_update_util()
to complete. Moreover, if they are updated to do that,
rcu_read_(un)lock() calls in cpufreq_update_util() might be
replaced with rcu_read_(un)lock_sched(), respectively, but
those aren't really necessary, because the scheduler calls
that function from RCU-sched read-side critical sections
already.

In addition to that, if cpufreq_set_update_util_data() checks
the func field in the struct update_util_data before setting
the per-CPU pointer to it, the data->func check may be dropped
from cpufreq_update_util() as well.

Make the above changes to reduce the overhead from
cpufreq_update_util() in the scheduler paths invoking it
and to make the cleanup after removing its callbacks less
heavy-weight somewhat.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

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cpufreq: intel_pstate: Replace timers with utilization update callbacks

Instead of using a per-CPU deferrable timer for utilization sampling
and P-states adjustments, register a utilization update c

cpufreq: intel_pstate: Replace timers with utilization update callbacks

Instead of using a per-CPU deferrable timer for utilization sampling
and P-states adjustments, register a utilization update callback that
will be invoked from the scheduler on utilization changes.

The sampling rate is still the same as what was used for the deferrable
timers, so the functional impact of this patch should not be significant.

Based on an earlier patch from Srinivas Pandruvada.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

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cpufreq: intel_pstate: disable HWP notifications

Disable HWP Interrupt notification before enabling HWP. Since we don't
have HWP interrupt handling for possible performance interrupts, there
is not

cpufreq: intel_pstate: disable HWP notifications

Disable HWP Interrupt notification before enabling HWP. Since we don't
have HWP interrupt handling for possible performance interrupts, there
is not much use of enabling HWP interrupts.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Enable HWP by default

If the processor supports HWP, enable it by default without checking
for the cpu model. This will allow to enable HWP in all supported
processors without

cpufreq: intel_pstate: Enable HWP by default

If the processor supports HWP, enable it by default without checking
for the cpu model. This will allow to enable HWP in all supported
processors without driver change.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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intel_pstate: Update frequencies of policy->cpus only from ->set_policy()

The intel-pstate driver is using intel_pstate_hwp_set() from two
separate paths, i.e. ->set_policy() callback and sysfs upda

intel_pstate: Update frequencies of policy->cpus only from ->set_policy()

The intel-pstate driver is using intel_pstate_hwp_set() from two
separate paths, i.e. ->set_policy() callback and sysfs update path for
the files present in /sys/devices/system/cpu/intel_pstate/ directory.

While an update to the sysfs path applies to all the CPUs being managed
by the driver (which essentially means all the online CPUs), the update
via the ->set_policy() callback applies to a smaller group of CPUs
managed by the policy for which ->set_policy() is called.

And so, intel_pstate_hwp_set() should update frequencies of only the
CPUs that are part of policy->cpus mask, while it is called from
->set_policy() callback.

In order to do that, add a parameter (cpumask) to intel_pstate_hwp_set()
and apply the frequency changes only to the concerned CPUs.

For ->set_policy() path, we are only concerned about policy->cpus, and
so policy->rwsem lock taken by the core prior to calling ->set_policy()
is enough to take care of any races. The larger lock acquired by
get_online_cpus() is required only for the updates to sysfs files.

Add another routine, intel_pstate_hwp_set_online_cpus(), and call it
from the sysfs update paths.

This also fixes a lockdep reported recently, where policy->rwsem and
get_online_cpus() could have been acquired in any order causing an ABBA
deadlock. The sequence of events leading to that was:

intel_pstate_init(...)
...cpufreq_online(...)
down_write(&policy->rwsem); // Locks policy->rwsem
...
cpufreq_init_policy(policy);
...intel_pstate_hwp_set();
get_online_cpus(); // Temporarily locks cpu_hotplug.lock
...
up_write(&policy->rwsem);

pm_suspend(...)
...disable_nonboot_cpus()
_cpu_down()
cpu_hotplug_begin(); // Locks cpu_hotplug.lock
__cpu_notify(CPU_DOWN_PREPARE, ...);
...cpufreq_offline_prepare();
down_write(&policy->rwsem); // Locks policy->rwsem

Reported-and-tested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Minor cleanup for FRAC_BITS

785ee27 ("cpufreq: intel_pstate: Fix limits->max_perf rounding error")
hardcodes the value of FRAC_BITS. This patch fixes that minor issue.

Fixes

cpufreq: intel_pstate: Minor cleanup for FRAC_BITS

785ee27 ("cpufreq: intel_pstate: Fix limits->max_perf rounding error")
hardcodes the value of FRAC_BITS. This patch fixes that minor issue.

Fixes: 785ee2788141 (cpufreq: intel_pstate: Fix limits->max_perf rounding error)
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Account for IO wait time

In cases where we have many IOs, the global load becomes low and the
load algorithm will decrease the requested P-State. Because of that,
the IOs over

cpufreq: intel_pstate: Account for IO wait time

In cases where we have many IOs, the global load becomes low and the
load algorithm will decrease the requested P-State. Because of that,
the IOs overheads will increase and impact the IO performances.

To improve IO bound work, we can count the io-wait time as busy time
in calculating CPU busy.

This change uses get_cpu_iowait_time_us() to obtain the IO wait time value
and converts time into number of cycles spent waiting on IO at the TSC
rate. At the moment, this trick is only used for Atom.

Signed-off-by: Philippe Longepe <philippe.longepe@intel.com>
Signed-off-by: Stephane Gasparini <stephane.gasparini@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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cpufreq: intel_pstate: Account for non C0 time

The current function to calculate cpu utilization uses the average P-state
ratio (APerf/Mperf) scaled by the ratio of the current P-state to the
max av

cpufreq: intel_pstate: Account for non C0 time

The current function to calculate cpu utilization uses the average P-state
ratio (APerf/Mperf) scaled by the ratio of the current P-state to the
max available non-turbo one. This leads to an overestimation of
utilization which causes higher-performance P-states to be selected more
often and that leads to increased energy consumption.

This is a problem for low-power systems, so it is better to use a
different utilization calculation algorithm for them.

Namely, the Percent Busy value (or load) can be estimated as the ratio of the
MPERF counter that runs at a constant rate only during active periods (C0) to
the time stamp counter (TSC) that also runs (at the same rate) during idle.
That is:

Percent Busy = 100 * (delta_mperf / delta_tsc)

Use this algorithm for platforms with SoCs based on the Airmont and Silvermont
Atom cores.

Signed-off-by: Philippe Longepe <philippe.longepe@intel.com>
Signed-off-by: Stephane Gasparini <stephane.gasparini@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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