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Subject[RFC 3/3] 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>
---
include/uapi/linux/sched.h | 4 +++-
include/uapi/linux/sched/types.h | 2 ++
kernel/sched/core.c | 15 +++++++++++++++
kernel/sched/sched.h | 1 +
4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index b3105ac1381a..73db430d11b6 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -71,6 +71,7 @@ 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)
@@ -82,6 +83,7 @@ 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..960774ac0c70 100644
--- a/include/uapi/linux/sched/types.h
+++ b/include/uapi/linux/sched/types.h
@@ -118,6 +118,8 @@ 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 ea7abbf5c1bb..dfd36ec14404 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4695,6 +4695,9 @@ 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);
+
+ /* Change latency tolerance of the task if !SCHED_FLAG_KEEP_PARAMS */
+ p->latency_tolerance = attr->sched_latency_tolerance;
}

/* Actually do priority change: must hold pi & rq lock. */
@@ -4852,6 +4855,13 @@ 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();

@@ -4886,6 +4896,9 @@ 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;
@@ -5392,6 +5405,8 @@ 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/kernel/sched/sched.h b/kernel/sched/sched.h
index 0db2c1b3361e..bb181175954b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -21,6 +21,7 @@
#include <linux/sched/nohz.h>
#include <linux/sched/numa_balancing.h>
#include <linux/sched/prio.h>
+#include <linux/sched/latency_tolerance.h>
#include <linux/sched/rt.h>
#include <linux/sched/signal.h>
#include <linux/sched/smt.h>
--
2.17.2
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