linux-kernel - [RFC PATCH 18/23] sched/task_struct: Add helpers for task classification

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Date:   Fri,  9 Sep 2022 16:12:00 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "Tim C . Chen" <tim.c.chen@...el.com>
Subject: [RFC PATCH 18/23] sched/task_struct: Add helpers for task classification

The unprocessed classification that hardware provides for a task may not
be usable by the scheduler. The classification may change too frequently.
An arch-specific implementation may want to consider other factors. For
instance, Intel Thread Director considers the state of the SMT siblings
of core.

Provide per-task helper variables that architectures can use to post-
process the classification that hardware provides.

Cc: Ben Segall <bsegall@...gle.com>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Len Brown <len.brown@...el.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Tim C. Chen <tim.c.chen@...el.com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
signed char and unsigned char are both signed in riscv architecture.
Use a signed char to avoid compilation warnings.
---
 include/linux/sched.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 73f9e745d17d..6c8907622f00 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1517,6 +1517,16 @@ struct task_struct {
 #ifdef CONFIG_SCHED_TASK_CLASSES
 	/* Class of task that the scheduler uses for task placement decisions */
 	short				class;
+	/*
+	 * A candidate classification that arch-specific implementations
+	 * qualify for correctness.
+	 */
+	short				class_candidate;
+	/*
+	 * Counter to filter out transient the candidate classification
+	 * of a task
+	 */
+	char				class_debounce_counter;
 #endif
 
 	/*
-- 
2.25.1