[PATCH v3 01/24] sched/task_struct: Introduce IPC classes of tasks

[Ricardo Neri]

On hybrid processors, the architecture differences between the types of
CPUs lead to different instructions-per-cycle (IPC) on each type of CPU.
IPCs may differ further by the type of instructions. Instructions can be
grouped into classes of similar IPCs.

Hence, tasks can be classified into groups based on the type of
instructions they execute.

Add a new member task_struct::ipcc to associate a particular task to
an IPC class that depends on the instructions it executes.

The scheduler may use the IPC class of a task and data about the
performance among CPUs of a given IPC class to improve throughput. It
may, for instance, place certain classes of tasks on CPUs of higher
performance.

The methods to determine the classification of a task and its relative
IPC score are specific to each CPU architecture.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Ionela Voinescu <ionela.voinescu@xxxxxxx>
Cc: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Lukasz Luba <lukasz.luba@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-pm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v2:
 * Changed the type of task_struct::ipcc to unsigned short. A subsequent
   patch uses bit fields to use 9 bits, along with other auxiliary
   members.

Changes since v1:
 * Renamed task_struct::class as task_struct::ipcc. (Joel)
 * Use task_struct::ipcc = 0 for unclassified tasks. (PeterZ)
 * Renamed CONFIG_SCHED_TASK_CLASSES as CONFIG_IPC_CLASSES. (PeterZ, Joel)
---
 include/linux/sched.h | 10 ++++++++++
 init/Kconfig          | 12 ++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4df2b3e76b30..98f84f90a01d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -127,6 +127,8 @@ struct task_group;
 					 __TASK_TRACED | EXIT_DEAD | EXIT_ZOMBIE | \
 					 TASK_PARKED)
 
+#define IPC_CLASS_UNCLASSIFIED		0
+
 #define task_is_running(task)		(READ_ONCE((task)->__state) == TASK_RUNNING)
 
 #define task_is_traced(task)		((READ_ONCE(task->jobctl) & JOBCTL_TRACED) != 0)
@@ -1528,6 +1530,14 @@ struct task_struct {
 	union rv_task_monitor		rv[RV_PER_TASK_MONITORS];
 #endif
 
+#ifdef CONFIG_IPC_CLASSES
+	/*
+	 * A hardware-defined classification of task that reflects but is
+	 * not identical to the number of instructions per cycle.
+	 */
+	unsigned short			ipcc;
+#endif
+
 	/*
 	 * New fields for task_struct should be added above here, so that
 	 * they are included in the randomized portion of task_struct.
diff --git a/init/Kconfig b/init/Kconfig
index e76dc579cfa2..731a4b652030 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -867,6 +867,18 @@ config UCLAMP_BUCKETS_COUNT
 
 	  If in doubt, use the default value.
 
+config IPC_CLASSES
+	bool "IPC classes of tasks"
+	depends on SMP
+	help
+	  If selected, each task is assigned a classification value that
+	  reflects the type of instructions that the task executes. This
+	  classification reflects but is not equal to the number of
+	  instructions retired per cycle.
+
+	  The scheduler uses the classification value to improve the placement
+	  of tasks.
+
 endmenu
 
 #
-- 
2.25.1