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Commit 97a13edc authored by Lina Iyer's avatar Lina Iyer Committed by Ram Chandrasekar
Browse files

drivers: cpu_cooling: Add core isolation as the last mitigation level 



When the CPUs are extremely hot, scaling frequency to the least in the
frequency table may not be sufficient to prevent a thermal runaway
condition and preserve junction integrity. The only safe option is to
isolate the core from the runnable set of CPUs and let the CPU cool
down, before tasking the CPU again.

Core-isolation is a scheduler feature that migrates the load off the CPU
and isolates the core from the runnable list. This is a faster
alternative to hotlpug.

Use Core-isolation as the last level of CPU cooling. CPU cooling device
should be careful when specifying the mitigation levels in the DT,
especially since core-isolation may happen if allowed even when the trip
temperature for this drastic mitigation is not even hit, resulting in
performance impact.

Change-Id: I7e2bb9cb35a16c9c3651ee432d0d74f396e17d55
Signed-off-by: default avatarLina Iyer <ilina@codeaurora.org>
parent c6b140d9

drivers/thermal/cpu_cooling.c

+15 −5
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
#include <linux/slab.h>

#include <linux/cpu.h>

#include <linux/cpu_cooling.h>

#include <linux/sched.h>



#include <trace/events/thermal.h>
@@ -45,6 +46,7 @@ 
 *	level 0 --> 1st Max Freq

 *	level 1 --> 2nd Max Freq

 *	...

 *	leven n --> core isolated

 */



/**
@@ -70,8 +72,8 @@ struct power_table { 
 *	cooling	devices.

 * @clipped_freq: integer value representing the absolute value of the clipped

 *	frequency.

 * @max_level: maximum cooling level. One less than total number of valid

 *	cpufreq frequencies.

 * @max_level: maximum cooling level. [0..max_level-1: <freq>

 *	max_level: Core unavailable]

 * @allowed_cpus: all the cpus involved for this cpufreq_cooling_device.

 * @node: list_head to link all cpufreq_cooling_device together.

 * @last_load: load measured by the latest call to cpufreq_get_requested_power()
@@ -162,7 +164,7 @@ static unsigned long get_level(struct cpufreq_cooling_device *cpufreq_dev, 
{

	unsigned long level;



	for (level = 0; level <= cpufreq_dev->max_level; level++) {

	for (level = 0; level < cpufreq_dev->max_level; level++) {

		if (freq == cpufreq_dev->freq_table[level])

			return level;
@@ -535,6 +537,12 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev, 
	if (cpufreq_device->cpufreq_state == state)

		return 0;



	/* If state is the last, isolate the CPU */

	if (state == cpufreq_device->max_level)

		return sched_isolate_cpu(cpu);

	else if (state < cpufreq_device->max_level)

		sched_unisolate_cpu(cpu);



	clip_freq = cpufreq_device->freq_table[state];

	cpufreq_device->cpufreq_state = state;

	cpufreq_device->clipped_freq = clip_freq;
@@ -848,7 +856,9 @@ __cpufreq_cooling_register(struct device_node *np, 
	cpufreq_for_each_valid_entry(pos, table)

		cpufreq_dev->max_level++;



	cpufreq_dev->freq_table = kmalloc(sizeof(*cpufreq_dev->freq_table) *

	/* Last level will indicate the core will be isolated. */

	cpufreq_dev->max_level++;

	cpufreq_dev->freq_table = kzalloc(sizeof(*cpufreq_dev->freq_table) *

					  cpufreq_dev->max_level, GFP_KERNEL);

	if (!cpufreq_dev->freq_table) {

		cool_dev = ERR_PTR(-ENOMEM);
@@ -881,7 +891,7 @@ __cpufreq_cooling_register(struct device_node *np, 
	}



	/* Fill freq-table in descending order of frequencies */

	for (i = 0, freq = -1; i <= cpufreq_dev->max_level; i++) {

	for (i = 0, freq = -1; i < cpufreq_dev->max_level; i++) {

		freq = find_next_max(table, freq);

		cpufreq_dev->freq_table[i] = freq;