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Subject[PATCH v2 3/3] sched: Allow sched_{get,set}attr to change latency_tolerance of the task
Date
Introduce the latency_tolerance attribute to sched_attr and provide a
mechanism to change the value with the use of sched_setattr/sched_getattr
syscall.

Also add new flag "SCHED_FLAG_LATENCY_TOLERANCE" to hint the change in
latency_tolerance of the task on every sched_setattr syscall.

Signed-off-by: Parth Shah <parth@linux.ibm.com>
Reviewed-by: Qais Yousef <qais.yousef@arm.com>
---
include/uapi/linux/sched.h | 4 +++-
include/uapi/linux/sched/types.h | 19 +++++++++++++++++++
kernel/sched/core.c | 17 +++++++++++++++++
tools/include/uapi/linux/sched.h | 4 +++-
4 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 25b4fa00bad1..a211d397e41d 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -101,6 +101,7 @@ struct clone_args {
#define SCHED_FLAG_KEEP_PARAMS 0x10
#define SCHED_FLAG_UTIL_CLAMP_MIN 0x20
#define SCHED_FLAG_UTIL_CLAMP_MAX 0x40
+#define SCHED_FLAG_LATENCY_TOLERANCE 0x80

#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
SCHED_FLAG_KEEP_PARAMS)
@@ -112,6 +113,7 @@ struct clone_args {
SCHED_FLAG_RECLAIM | \
SCHED_FLAG_DL_OVERRUN | \
SCHED_FLAG_KEEP_ALL | \
- SCHED_FLAG_UTIL_CLAMP)
+ SCHED_FLAG_UTIL_CLAMP | \
+ SCHED_FLAG_LATENCY_TOLERANCE)

#endif /* _UAPI_LINUX_SCHED_H */
diff --git a/include/uapi/linux/sched/types.h b/include/uapi/linux/sched/types.h
index c852153ddb0d..4f169c88517f 100644
--- a/include/uapi/linux/sched/types.h
+++ b/include/uapi/linux/sched/types.h
@@ -10,6 +10,7 @@ struct sched_param {

#define SCHED_ATTR_SIZE_VER0 48 /* sizeof first published struct */
#define SCHED_ATTR_SIZE_VER1 56 /* add: util_{min,max} */
+#define SCHED_ATTR_SIZE_VER2 60 /* add: latency_tolerance */

/*
* Extended scheduling parameters data structure.
@@ -96,6 +97,22 @@ struct sched_param {
* on a CPU with a capacity big enough to fit the specified value.
* A task with a max utilization value smaller than 1024 is more likely
* scheduled on a CPU with no more capacity than the specified value.
+ *
+ * Latency Tolerance Attributes
+ * ===========================
+ *
+ * A subset of sched_attr attributes allows to specify the relative latency
+ * requirements of a task with respect to the other tasks running/queued in the
+ * system.
+ *
+ * @ sched_latency_tolerance task's latency_tolerance value
+ *
+ * The latency_tolerance of a task can have any value in a range of
+ * [LATENCY_TOLERANCE_MIN..LATENCY_TOLERANCE_MAX].
+ *
+ * A task with latency_tolerance with the value of LATENCY_TOLERANCE_MIN can be
+ * taken for a task with lower latency requirements as opposed to the task with
+ * higher latency_tolerance.
*/
struct sched_attr {
__u32 size;
@@ -118,6 +135,8 @@ struct sched_attr {
__u32 sched_util_min;
__u32 sched_util_max;

+ /* latency requirement hints */
+ __s32 sched_latency_tolerance;
};

#endif /* _UAPI_LINUX_SCHED_TYPES_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3f9359d0e326..bc8a260223f6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4706,6 +4706,8 @@ static void __setscheduler_params(struct task_struct *p,
p->rt_priority = attr->sched_priority;
p->normal_prio = normal_prio(p);
set_load_weight(p, true);
+
+ p->latency_tolerance = attr->sched_latency_tolerance;
}

/* Actually do priority change: must hold pi & rq lock. */
@@ -4863,6 +4865,13 @@ static int __sched_setscheduler(struct task_struct *p,
return retval;
}

+ if (attr->sched_flags & SCHED_FLAG_LATENCY_TOLERANCE) {
+ if (attr->sched_latency_tolerance > MAX_LATENCY_TOLERANCE)
+ return -EINVAL;
+ if (attr->sched_latency_tolerance < MIN_LATENCY_TOLERANCE)
+ return -EINVAL;
+ }
+
if (pi)
cpuset_read_lock();

@@ -4897,6 +4906,9 @@ static int __sched_setscheduler(struct task_struct *p,
goto change;
if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
goto change;
+ if (attr->sched_flags & SCHED_FLAG_LATENCY_TOLERANCE &&
+ attr->sched_latency_tolerance != p->latency_tolerance)
+ goto change;

p->sched_reset_on_fork = reset_on_fork;
retval = 0;
@@ -5145,6 +5157,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
size < SCHED_ATTR_SIZE_VER1)
return -EINVAL;

+ if ((attr->sched_flags & SCHED_FLAG_LATENCY_TOLERANCE) &&
+ size < SCHED_ATTR_SIZE_VER2)
+ return -EINVAL;
/*
* XXX: Do we want to be lenient like existing syscalls; or do we want
* to be strict and return an error on out-of-bounds values?
@@ -5374,6 +5389,8 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
else
kattr.sched_nice = task_nice(p);

+ kattr.sched_latency_tolerance = p->latency_tolerance;
+
#ifdef CONFIG_UCLAMP_TASK
kattr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
kattr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
diff --git a/tools/include/uapi/linux/sched.h b/tools/include/uapi/linux/sched.h
index 99335e1f4a27..5ce62b1be196 100644
--- a/tools/include/uapi/linux/sched.h
+++ b/tools/include/uapi/linux/sched.h
@@ -97,6 +97,7 @@ struct clone_args {
#define SCHED_FLAG_KEEP_PARAMS 0x10
#define SCHED_FLAG_UTIL_CLAMP_MIN 0x20
#define SCHED_FLAG_UTIL_CLAMP_MAX 0x40
+#define SCHED_FLAG_LATENCY_TOLERANCE 0X80

#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
SCHED_FLAG_KEEP_PARAMS)
@@ -108,6 +109,7 @@ struct clone_args {
SCHED_FLAG_RECLAIM | \
SCHED_FLAG_DL_OVERRUN | \
SCHED_FLAG_KEEP_ALL | \
- SCHED_FLAG_UTIL_CLAMP)
+ SCHED_FLAG_UTIL_CLAMP | \
+ SCHED_FLAG_LATENCY_TOLERANCE)

#endif /* _UAPI_LINUX_SCHED_H */
--
2.17.2
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