The cpufreq core and governors aren't supposed to set a limit on how
fast we want to try changing the frequency. This is currently done for
the legacy governors with help of min_sampling_rate.

At worst, we may end up setting the sampling rate to a value lower than
the rate at which frequency can be changed and then one of the CPUs in
the policy will be only changing frequency for ever.

But that is something for the user to decide and there is no need to
have special handling for such cases in the core. Leave it for the user
to figure out.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

We are going to split <linux/sched/cpufreq.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/cpufreq.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Conservative governor changes the CPU frequency in steps.
That means that if a CPU runs at max frequency, it will need several
sampling periods to return to min frequency when the workload
is finished.

If the update function that calculates the load and target frequency
is deferred, the governor might need even more time to decrease the
frequency.

This may have impact to power consumption and after all conservative
should decrease the frequency if there is no workload at every sampling
rate.

To resolve the above issue calculate the number of sampling periods
that the update is deferred. Considering that for each sampling period
conservative should drop the frequency by a freq_step because the
CPU was idle apply the proper subtraction to requested frequency.

Below, the kernel trace with and without this patch. First an
intensive workload is applied on a specific CPU. Then the workload
is removed and the CPU goes to idle.

WITHOUT

     <idle>-0     [007] dN..   620.329153: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   620.350857: cpu_frequency: state=1700000 cpu_id=7
kworker/7:2-556   [007] ....   620.370856: cpu_frequency: state=1900000 cpu_id=7
kworker/7:2-556   [007] ....   620.390854: cpu_frequency: state=2100000 cpu_id=7
kworker/7:2-556   [007] ....   620.411853: cpu_frequency: state=2200000 cpu_id=7
kworker/7:2-556   [007] ....   620.432854: cpu_frequency: state=2400000 cpu_id=7
kworker/7:2-556   [007] ....   620.453854: cpu_frequency: state=2600000 cpu_id=7
kworker/7:2-556   [007] ....   620.494856: cpu_frequency: state=2900000 cpu_id=7
kworker/7:2-556   [007] ....   620.515856: cpu_frequency: state=3100000 cpu_id=7
kworker/7:2-556   [007] ....   620.536858: cpu_frequency: state=3300000 cpu_id=7
kworker/7:2-556   [007] ....   620.557857: cpu_frequency: state=3401000 cpu_id=7
     <idle>-0     [007] d...   669.591363: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   669.591939: cpu_idle: state=4294967295 cpu_id=7
     <idle>-0     [007] d...   669.591980: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] dN..   669.591989: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   670.201224: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   670.221975: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   670.222016: cpu_frequency: state=3300000 cpu_id=7
     <idle>-0     [007] d...   670.222026: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   670.234964: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   670.801251: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   671.236046: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   671.236073: cpu_frequency: state=3100000 cpu_id=7
     <idle>-0     [007] d...   671.236112: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   671.393437: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   671.401277: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   671.404083: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   671.404111: cpu_frequency: state=2900000 cpu_id=7
     <idle>-0     [007] d...   671.404125: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   671.404974: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   671.501180: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   671.995414: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   671.995459: cpu_frequency: state=2800000 cpu_id=7
     <idle>-0     [007] d...   671.995469: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   671.996287: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   672.001305: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.078374: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   672.078410: cpu_frequency: state=2600000 cpu_id=7
     <idle>-0     [007] d...   672.078419: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.158020: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   672.158040: cpu_frequency: state=2400000 cpu_id=7
     <idle>-0     [007] d...   672.158044: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.160038: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   672.234557: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.237121: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   672.237174: cpu_frequency: state=2100000 cpu_id=7
     <idle>-0     [007] d...   672.237186: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.237778: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   672.267902: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.269860: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   672.269906: cpu_frequency: state=1900000 cpu_id=7
     <idle>-0     [007] d...   672.269914: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.271902: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...   672.751342: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...   672.823056: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556   [007] ....   672.823095: cpu_frequency: state=1600000 cpu_id=7

WITH

     <idle>-0     [007] dN..  4380.928009: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399   [007] ....  4380.949767: cpu_frequency: state=2000000 cpu_id=7
kworker/7:2-399   [007] ....  4380.969765: cpu_frequency: state=2200000 cpu_id=7
kworker/7:2-399   [007] ....  4381.009766: cpu_frequency: state=2500000 cpu_id=7
kworker/7:2-399   [007] ....  4381.029767: cpu_frequency: state=2600000 cpu_id=7
kworker/7:2-399   [007] ....  4381.049769: cpu_frequency: state=2800000 cpu_id=7
kworker/7:2-399   [007] ....  4381.069769: cpu_frequency: state=3000000 cpu_id=7
kworker/7:2-399   [007] ....  4381.089771: cpu_frequency: state=3100000 cpu_id=7
kworker/7:2-399   [007] ....  4381.109772: cpu_frequency: state=3400000 cpu_id=7
kworker/7:2-399   [007] ....  4381.129773: cpu_frequency: state=3401000 cpu_id=7
     <idle>-0     [007] d...  4428.226159: cpu_idle: state=1 cpu_id=7
     <idle>-0     [007] d...  4428.226176: cpu_idle: state=4294967295 cpu_id=7
     <idle>-0     [007] d...  4428.226181: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...  4428.227177: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...  4428.551640: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...  4428.649239: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399   [007] ....  4428.649268: cpu_frequency: state=2800000 cpu_id=7
     <idle>-0     [007] d...  4428.649278: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...  4428.689856: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...  4428.799542: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...  4428.801683: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399   [007] ....  4428.801748: cpu_frequency: state=1700000 cpu_id=7
     <idle>-0     [007] d...  4428.801761: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...  4428.806545: cpu_idle: state=4294967295 cpu_id=7
...
     <idle>-0     [007] d...  4429.051880: cpu_idle: state=4 cpu_id=7
     <idle>-0     [007] d...  4429.086240: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399   [007] ....  4429.086293: cpu_frequency: state=1600000 cpu_id=7

Without the patch the CPU dropped to min frequency after 3.2s
With the patch applied the CPU dropped to min frequency after 0.86s
Signed-off-by: NStratos Karafotis <stratosk@semaphore.gr>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The earlier implementation of governors used background timers and so
functions, mutex, etc had 'timer' keyword in their names.

But that's not true anymore. Replace 'timer' with 'update', as those
functions, variables are based around updates to frequency.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The 'initialized' field in struct cpufreq_governor is only used by
the conservative governor (as a usage counter) and the way that
happens is far from straightforward and arguably incorrect.

Namely, the value of 'initialized' is checked by
cpufreq_dbs_governor_init() and cpufreq_dbs_governor_exit() and
the results of those checks are passed (as the second argument) to
the ->init() and ->exit() callbacks in struct dbs_governor.  Those
callbacks are only implemented by the ondemand and conservative
governors and ondemand doesn't use their second argument at all.
In turn, the conservative governor uses it to decide whether or not
to either register or unregister a transition notifier.

That whole mechanism is not only unnecessarily convoluted, but also
racy, because the 'initialized' field of struct cpufreq_governor is
updated in cpufreq_init_governor() and cpufreq_exit_governor() under
policy->rwsem which doesn't help if one of these functions is run
twice in parallel for different policies (which isn't impossible in
principle), for example.

Instead of it, add a proper usage counter to the conservative
governor and update it from cs_init() and cs_exit() which is
guaranteed to be non-racy, as those functions are only called
under gov_dbs_data_mutex which is global.

With that in place, drop the 'initialized' field from struct
cpufreq_governor as it is not used any more.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The design of the cpufreq governor API is not very straightforward,
as struct cpufreq_governor provides only one callback to be invoked
from different code paths for different purposes.  The purpose it is
invoked for is determined by its second "event" argument, causing it
to act as a "callback multiplexer" of sorts.

Unfortunately, that leads to extra complexity in governors, some of
which implement the ->governor() callback as a switch statement
that simply checks the event argument and invokes a separate function
to handle that specific event.

That extra complexity can be eliminated by replacing the all-purpose
->governor() callback with a family of callbacks to carry out specific
governor operations: initialization and exit, start and stop and policy
limits updates.  That also turns out to reduce the code size too, so
do it.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The name of the prev_cpu_wall field in struct cpu_dbs_info is
confusing, because it doesn't represent wall time, but the previous
update time as returned by get_cpu_idle_time() (that may be the
current value of jiffies_64 in some cases, for example).

Moreover, the names of some related variables in dbs_update() take
that confusion further.

Rename all of those things to make their names reflect the purpose
more accurately.  While at it, drop unnecessary parens from one of
the updated expressions.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NChen Yu <yu.c.chen@intel.com>

Move definitions of symbols related to transition latency and
sampling rate to include/linux/cpufreq.h so they can be used by
(future) goverernors located outside of drivers/cpufreq/.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Move definitions and function headers related to struct gov_attr_set
to include/linux/cpufreq.h so they can be used by (future) goverernors
located outside of drivers/cpufreq/.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Move abstract code related to struct gov_attr_set to a separate (new)
file so it can be shared with (future) goverernors that won't share
more code with "ondemand" and "conservative".

No intentional functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

In addition to fields representing governor tunables, struct dbs_data
contains some fields needed for the management of objects of that
type.  As it turns out, that part of struct dbs_data may be shared
with (future) governors that won't use the common code used by
"ondemand" and "conservative", so move it to a separate struct type
and modify the code using struct dbs_data to follow.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

That mutex is only used by cpufreq_governor_dbs() and it doesn't
need to be exported to modules, so make it static and drop the
export incantation.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Move the definitions of struct od_dbs_tuners and struct cs_dbs_tuners
from the common governor header to the ondemand and conservative
governor code, respectively, as they don't need to be in the common
header any more.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

After previous changes there is only one piece of code in the
ondemand governor making references to per-CPU data structures,
but it can be easily modified to avoid doing that, so modify it
accordingly and move the definition of per-CPU data used by the
ondemand and conservative governors to the common code.  Next,
change that code to access the per-CPU data structures directly
rather than via a governor callback.

This causes the ->get_cpu_cdbs governor callback to become
unnecessary, so drop it along with the macro and function
definitions related to it.

Finally, drop the definitions of struct od_cpu_dbs_info_s and
struct cs_cpu_dbs_info_s that aren't necessary any more.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Some fields in struct od_cpu_dbs_info_s and struct cs_cpu_dbs_info_s
are only used for a limited set of CPUs.  Namely, if a policy is
shared between multiple CPUs, those fields will only be used for one
of them (policy->cpu).  This means that they really are per-policy
rather than per-CPU and holding room for them in per-CPU data
structures is generally wasteful.  Also moving those fields into
per-policy data structures will allow some significant simplifications
to be made going forward.

For this reason, introduce struct cs_policy_dbs_info and
struct od_policy_dbs_info to hold those fields.  Define each of the
new structures as an extension of struct policy_dbs_info (such that
struct policy_dbs_info is embedded in each of them) and introduce
new ->alloc and ->free governor callbacks to allocate and free
those structures, respectively, such that ->alloc() will return
a pointer to the struct policy_dbs_info embedded in the allocated
data structure and ->free() will take that pointer as its argument.

With that, modify the code accessing the data fields in question
in per-CPU data objects to look for them in the new structures
via the struct policy_dbs_info pointer available to it and drop
them from struct od_cpu_dbs_info_s and struct cs_cpu_dbs_info_s.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The ->store() callbacks of some tunable sysfs attributes of the
ondemand and conservative governors trigger immediate updates of
the CPU load information for all CPUs "governed" by the given
dbs_data by walking the cpu_dbs_info structures for all online
CPUs in the system and updating them.

This is questionable for two reasons.  First, it may lead to a lot of
extra overhead on a system with many CPUs if the given dbs_data is
only associated with a few of them.  Second, if governor tunables are
per-policy, the CPUs associated with the other sets of governor
tunables should not be updated.

To address this issue, use the observation that in all of the places
in question the update operation may be carried out in the same way
(because all of the tunables involved are now located in struct
dbs_data and readily available to the common code) and make the
code in those places invoke the same (new) helper function that
will carry out the update correctly.

That new function always checks the ignore_nice_load tunable value
and updates the CPUs' prev_cpu_nice data fields if that's set, which
wasn't done by the original code in store_io_is_busy(), but it
should have been done in there too.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The ->powersave_bias_init_cpu callback in struct od_ops is only used
in one place and that invocation may be replaced with a direct call
to the function pointed to by that callback, so change the code
accordingly and drop the callback.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

After some previous changes, the ->get_cpu_dbs_info_s governor
callback and the "governor" field in struct dbs_governor (whose
value represents the governor type) are not used any more, so
drop them.

Also drop the unused gov_ops field from struct dbs_governor.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

To avoid having to check the governor type explicitly in the common
code in order to initialize data structures specific to the governor
type properly, add a ->start callback to struct dbs_governor and
use it to initialize those data structures for the ondemand and
conservative governors.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The io_is_busy governor tunable is only used by the ondemand governor
and is located in the ondemand-specific data structure, but it is
looked at by the common governor code that has to do ugly things to
get to that value, so move it to struct dbs_data and modify ondemand
accordingly.

Since the conservative governor never touches that field, it will
be always 0 for that governor and it won't have any effect on the
results of computations in that case.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The ->freq_increase callback in struct od_ops is never invoked,
so drop it.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Do not convert microseconds to jiffies and the other way around
in governor computations related to the sampling rate and sample
delay and drop delay_for_sampling_rate() which isn't of any use
then.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The rate_mult field in struct od_cpu_dbs_info_s is used by the code
shared with the conservative governor and to access it that code
has to do an ugly governor type check.  However, first of all it
is ever only used for policy->cpu, so it is per-policy rather than
per-CPU and second, it is initialized to 1 by cpufreq_governor_start(),
so if the conservative governor never modifies it, it will have no
effect on the results of any computations.

For these reasons, move rate_mult to struct policy_dbs_info (as a
common field).
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The way the ->gov_check_cpu governor callback is used by the ondemand
and conservative governors is not really straightforward.  Namely, the
governor calls dbs_check_cpu() that updates the load information for
the policy and the invokes ->gov_check_cpu() for the governor.

To get rid of that entanglement, notice that cpufreq_governor_limits()
doesn't need to call dbs_check_cpu() directly.  Instead, it can simply
reset the sample delay to 0 which will cause a sample to be taken
immediately.  The result of that is practically equivalent to calling
dbs_check_cpu() except that it will trigger a full update of governor
internal state and not just the ->gov_check_cpu() part.

Following that observation, make cpufreq_governor_limits() reset
the sample delay and turn dbs_check_cpu() into a function that will
simply evaluate the load and return the result called dbs_update().

That function can now be called by governors from the routines that
previously were pointed to by ->gov_check_cpu and those routines
can be called directly by each governor instead of dbs_check_cpu().
This way ->gov_check_cpu becomes unnecessary, so drop it.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Rework the handling of work items by dbs_update_util_handler() and
dbs_work_handler() so the former (which is executed in scheduler
paths) only uses atomic operations when absolutely necessary.  That
is, when the policy is shared and dbs_update_util_handler() has
already decided that this is the time to queue up a work item.

In particular, this avoids the atomic ops entirely on platforms where
policy objects are never shared.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The ondemand governor already updates sample_delay_ns immediately on
updates to the sampling rate, but conservative doesn't do that.

It was left out earlier as the code was really too complex to get
that done easily.  Things are sorted out very well now, however, and
the conservative governor can be modified to follow ondemand in that
respect.

Moreover, since the code needed to implement that in the
conservative governor would be identical to the corresponding
ondemand governor's code, make that code common and change both
governors to use it.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NJuri Lelli <juri.lelli@arm.com>
Tested-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

We used to drop policy->rwsem just before calling __cpufreq_governor()
in some cases earlier and so it was possible that __cpufreq_governor()
ran concurrently via separate threads for the same policy.

In order to guarantee valid state transitions for governors,
'governor_enabled' was required to be protected using some locking
and cpufreq_governor_lock was added for that.

But now __cpufreq_governor() is always called under policy->rwsem,
and 'governor_enabled' is protected against races even without
cpufreq_governor_lock.

Get rid of the extra lock now.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NJuri Lelli <juri.lelli@arm.com>
Tested-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw : Changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The dbs_data_mutex lock is currently used in two places.  First,
cpufreq_governor_dbs() uses it to guarantee mutual exclusion between
invocations of governor operations from the core.  Second, it is used by
ondemand governor's update_sampling_rate() to ensure the stability of
data structures walked by it.

The second usage is quite problematic, because update_sampling_rate() is
called from a governor sysfs attribute's ->store callback and that leads
to a deadlock scenario involving cpufreq_governor_exit() which runs
under dbs_data_mutex.  Thus it is better to rework the code so
update_sampling_rate() doesn't need to acquire dbs_data_mutex.

To that end, rework update_sampling_rate() to walk a list of policy_dbs
objects supported by the dbs_data one it has been called for (instead of
walking cpu_dbs_info object for all CPUs).  The list manipulation is
protected with dbs_data->mutex which also is held around the execution
of update_sampling_rate(), it is not necessary to hold dbs_data_mutex in
that function any more.
Reported-by: NJuri Lelli <juri.lelli@arm.com>
Reported-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
[ rjw: Subject & changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The previous commit introduced a new set of macros for creating sysfs
attributes that represent governor tunables and the old macros used for
this purpose are not needed any more, so drop them.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NJuri Lelli <juri.lelli@arm.com>
Tested-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Subject & changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The ondemand and conservative governors use the global-attr or freq-attr
structures to represent sysfs attributes corresponding to their tunables
(which of them is actually used depends on whether or not different
policy objects can use the same governor with different tunables at the
same time and, consequently, on where those attributes are located in
sysfs).

Unfortunately, in the freq-attr case, the standard cpufreq show/store
sysfs attribute callbacks are applied to the governor tunable attributes
and they always acquire the policy->rwsem lock before carrying out the
operation.  That may lead to an ABBA deadlock if governor tunable
attributes are removed under policy->rwsem while one of them is being
accessed concurrently (if sysfs attributes removal wins the race, it
will wait for the access to complete with policy->rwsem held while the
attribute callback will block on policy->rwsem indefinitely).

We attempted to address this issue by dropping policy->rwsem around
governor tunable attributes removal (that is, around invocations of the
->governor callback with the event arg equal to CPUFREQ_GOV_POLICY_EXIT)
in cpufreq_set_policy(), but that opened up race conditions that had not
been possible with policy->rwsem held all the time.  Therefore
policy->rwsem cannot be dropped in cpufreq_set_policy() at any point,
but the deadlock situation described above must be avoided too.

To that end, use the observation that in principle governor tunables may
be represented by the same data type regardless of whether the governor
is system-wide or per-policy and introduce a new structure, struct
governor_attr, for representing them and new corresponding macros for
creating show/store sysfs callbacks for them.  Also make their parent
kobject use a new kobject type whose default show/store callbacks are
not related to the standard core cpufreq ones in any way (and they don't
acquire policy->rwsem in particular).
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NJuri Lelli <juri.lelli@arm.com>
Tested-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Subject & changelog + rebase ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

There are a few common tunables shared between the ondemand and
conservative governors.  Move them to struct dbs_data to simplify
code.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NJuri Lelli <juri.lelli@arm.com>
Tested-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

Some tunables are present in governor-specific structures, whereas one
(min_sampling_rate) is located directly in struct dbs_data.

There is a special macro for creating its sysfs attribute and the
show/store callbacks, but since more tunables are going to be moved
to struct dbs_data, a new generic macro for such cases will be useful,
so add it and use it for min_sampling_rate.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Tested-by: NJuri Lelli <juri.lelli@arm.com>
Tested-by: NShilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
[ rjw: Subject & changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

The skip_work field in struct policy_dbs_info technically is a
counter, so give it a new name to reflect that.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The struct policy_dbs_info objects representing per-policy governor
data are not accessible directly from the corresponding policy
objects.  To access them, one has to get a pointer to the
struct cpu_dbs_info of policy->cpu and use the policy_dbs field of
that which isn't really straightforward.

To address that rearrange the governor data structures so the
governor_data pointer in struct cpufreq_policy will point to
struct policy_dbs_info (instead of struct dbs_data) and that will
contain a pointer to struct dbs_data.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Since policy->cpu is always passed as the second argument to
dbs_check_cpu(), it is not really necessary to pass it, because
the function can obtain that value via its first argument just fine.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The struct cpu_common_dbs_info structure represents the per-policy
part of the governor data (for the ondemand and conservative
governors), but its name doesn't reflect its purpose.

Rename it to struct policy_dbs_info and rename variables related to
it accordingly.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Since it is possible to obtain a pointer to struct dbs_governor
from a pointer to the struct governor embedded in it with the help
of container_of(), the additional gov pointer in struct dbs_data
isn't really necessary.

Drop that pointer and make the code using it reach the dbs_governor
object via policy->governor.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

Since it is possible to obtain a pointer to struct dbs_governor
from a pointer to the struct governor embedded in it via
container_of(), the second argument of cpufreq_governor_init()
is not necessary.  Accordingly, cpufreq_governor_dbs() doesn't
need its second argument either and the ->governor callbacks
for both the ondemand and conservative governors may be set
to cpufreq_governor_dbs() directly.  Make that happen.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NSaravana Kannan <skannan@codeaurora.org>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

The ondemand and conservative governors are represented by
struct common_dbs_data whose name doesn't reflect the purpose it
is used for, so rename it to struct dbs_governor and rename
variables of that type accordingly.

No functional changes.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>

For the ondemand and conservative governors (generally, governors
that use the common code in cpufreq_governor.c), there are two static
data structures representing the governor, the struct governor
structure (the interface to the cpufreq core) and the struct
common_dbs_data one (the interface to the cpufreq_governor.c code).

There's no fundamental reason why those two structures have to be
separate.  Moreover, if the struct governor one is included into
struct common_dbs_data, it will be possible to reach the latter from
the policy via its policy->governor pointer, so it won't be necessary
to pass a separate pointer to it around.  For this reason, embed
struct governor in struct common_dbs_data.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NSaravana Kannan <skannan@codeaurora.org>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>