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Subject[PATCH v4 1/4] sched: Introduce latency-nice as a per-task attribute
Date
Latency-nice 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_nice = -20 indicates the task to have the least latency as
compared to the tasks having latency_nice = +19.

The latency_nice 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 467d26046416..0668948fddcd 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_nice;

const struct sched_class *sched_class;
struct sched_entity se;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 878910e8b299..26b9758075e4 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 nice is meant to provide scheduler hints about the relative
+ * latency requirements of a task with respect to other tasks.
+ * Thus a task with latency_nice == 19 can be hinted as the task with no
+ * latency requirements, in contrast to the task with latency_nice == -20
+ * which should be given priority in terms of lower latency.
+ */
+#define MAX_LATENCY_NICE 19
+#define MIN_LATENCY_NICE -20
+
+#define LATENCY_NICE_WIDTH \
+ (MAX_LATENCY_NICE - MIN_LATENCY_NICE + 1)
+
+/*
+ * Default tasks should be treated as a task with latency_nice = 0.
+ */
+#define DEFAULT_LATENCY_NICE 0
+
/*
* Increase resolution of nice-level calculations for 64-bit architectures.
* The extra resolution improves shares distribution and load balancing of
--
2.17.2
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