[PATCH v4 01/24] sched/task_struct: Introduce IPC classes of tasks

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

On hybrid processors, the architecture differences between the types of
CPUs result in different instructions-per-cycle (IPC) rates for each type
of CPU. IPCs may vary further by the type of instructions being executed.
Instructions can be grouped into classes of similar IPCs.

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@google.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Lukasz Luba <lukasz.luba@arm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Perry Yuan <Perry.Yuan@amd.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tim C. Chen <tim.c.chen@intel.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Zhao Liu <zhao1.liu@linux.intel.com>
Cc: x86@kernel.org
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
Changes since v3:
 * None

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 1292d38d66cc..9fdee040f450 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -129,6 +129,8 @@ struct user_event_mm;
 					 __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)
@@ -1534,6 +1536,14 @@ struct task_struct {
 	struct user_event_mm		*user_event_mm;
 #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 32c24950c4ce..ea3371ccb530 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -839,6 +839,18 @@ 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