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From:   Parth Shah <parth@linux.ibm.com>
To:     linux-kernel@vger.kernel.org
Cc:     peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org,
        patrick.bellasi@matbug.net, valentin.schneider@arm.com,
        qais.yousef@arm.com, pavel@ucw.cz, dhaval.giani@oracle.com,
        qperret@qperret.net, David.Laight@ACULAB.COM, pjt@google.com,
        tj@kernel.org, dietmar.eggemann@arm.com
Subject: [PATCH v2 1/3] sched: Introduce latency-tolerance as a per-task attribute
Date:   Sun,  8 Dec 2019 11:34:08 +0530
In-Reply-To: <20191208060410.17814-1-parth@linux.ibm.com>
References: <20191208060410.17814-1-parth@linux.ibm.com>
Message-Id: <20191208060410.17814-2-parth@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Latency-tolerance indicates the latency requirements of a task with respect
to the other tasks in the system. The value of the attribute can be within
the range of [-20, 19] both inclusive to be in-line with the values just
like task nice values.

latency_tolerance = -20 indicates the task to have the least latency as
compared to the tasks having latency_tolerance = +19.

The latency_tolerance may affect only the CFS SCHED_CLASS by getting
latency requirements from the userspace.

Signed-off-by: Parth Shah <parth@linux.ibm.com>
Reviewed-by: Qais Yousef <qais.yousef@arm.com>
---
 include/linux/sched.h |  1 +
 kernel/sched/sched.h  | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 84b26d38c929..d5f907d7a91a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -676,6 +676,7 @@ struct task_struct {
 	int				static_prio;
 	int				normal_prio;
 	unsigned int			rt_priority;
+	int				latency_tolerance;
 
 	const struct sched_class	*sched_class;
 	struct sched_entity		se;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 280a3c735935..3d68aaad02cc 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -101,6 +101,24 @@ extern long calc_load_fold_active(struct rq *this_rq, long adjust);
  */
 #define NS_TO_JIFFIES(TIME)	((unsigned long)(TIME) / (NSEC_PER_SEC / HZ))
 
+/*
+ * Latency tolerance is meant to provide scheduler hints about the relative
+ * latency requirements of a task with respect to other tasks.
+ * Thus a task with latency_tolerance == 19 can be hinted as the task with no
+ * latency requirements, in contrast to the task with latency_tolerance == -20
+ * which should be given priority in terms of lower latency.
+ */
+#define MAX_LATENCY_TOLERANCE	19
+#define MIN_LATENCY_TOLERANCE	-20
+
+#define LATENCY_TOLERANCE_WIDTH	\
+	(MAX_LATENCY_TOLERANCE - MIN_LATENCY_TOLERANCE + 1)
+
+/*
+ * Default tasks should be treated as a task with latency_tolerance = 0.
+ */
+#define DEFAULT_LATENCY_TOLERANCE	0
+
 /*
  * Increase resolution of nice-level calculations for 64-bit architectures.
  * The extra resolution improves shares distribution and load balancing of
-- 
2.17.2