[PATCH v7 4/9] sched: Allow sched_{get,set}attr to change latency_nice of the task

Vincent Guittot
2022-10-28T09:35:29Z

From: Parth Shah <parth@linux.ibm.com>

Introduce the latency_nice 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_NICE" to hint the change in
latency_nice of the task on every sched_setattr syscall.

Signed-off-by: Parth Shah <parth@linux.ibm.com>
[rebase and add a dedicated __setscheduler_latency ]
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
include/uapi/linux/sched.h | 4 +++-
include/uapi/linux/sched/types.h | 19 +++++++++++++++++++
kernel/sched/core.c | 24 ++++++++++++++++++++++++
tools/include/uapi/linux/sched.h | 4 +++-
4 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 3bac0a8ceab2..b2e932c25be6 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -132,6 +132,7 @@ 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_NICE 0x80

#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
SCHED_FLAG_KEEP_PARAMS)
@@ -143,6 +144,7 @@ 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_NICE)

#endif /* _UAPI_LINUX_SCHED_H */
diff --git a/include/uapi/linux/sched/types.h b/include/uapi/linux/sched/types.h
index f2c4589d4dbf..db1e8199e8c8 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_nice */

/*
* Extended scheduling parameters data structure.
@@ -98,6 +99,22 @@ struct sched_param {
* scheduled on a CPU with no more capacity than the specified value.
*
* A task utilization boundary can be reset by setting the attribute to -1.
+ *
+ * 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_nice task's latency_nice value
+ *
+ * The latency_nice of a task can have any value in a range of
+ * [MIN_LATENCY_NICE..MAX_LATENCY_NICE].
+ *
+ * A task with latency_nice with the value of LATENCY_NICE_MIN can be
+ * taken for a task requiring a lower latency as opposed to the task with
+ * higher latency_nice.
*/
struct sched_attr {
__u32 size;
@@ -120,6 +137,8 @@ struct sched_attr {
__u32 sched_util_min;
__u32 sched_util_max;

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

#endif /* _UAPI_LINUX_SCHED_TYPES_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 54544353025b..b2accc9da4fe 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7318,6 +7318,14 @@ 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);
+
+}
+
+static void __setscheduler_latency(struct task_struct *p,
+ const struct sched_attr *attr)
+{
+ if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE)
+ p->latency_nice = attr->sched_latency_nice;
}

/*
@@ -7460,6 +7468,13 @@ static int __sched_setscheduler(struct task_struct *p,
return retval;
}

+ if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE) {
+ if (attr->sched_latency_nice > MAX_LATENCY_NICE)
+ return -EINVAL;
+ if (attr->sched_latency_nice < MIN_LATENCY_NICE)
+ return -EINVAL;
+ }
+
if (pi)
cpuset_read_lock();

@@ -7494,6 +7509,9 @@ 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_NICE &&
+ attr->sched_latency_nice != p->latency_nice)
+ goto change;

p->sched_reset_on_fork = reset_on_fork;
retval = 0;
@@ -7582,6 +7600,7 @@ static int __sched_setscheduler(struct task_struct *p,
__setscheduler_params(p, attr);
__setscheduler_prio(p, newprio);
}
+ __setscheduler_latency(p, attr);
__setscheduler_uclamp(p, attr);

if (queued) {
@@ -7792,6 +7811,9 @@ 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_NICE) &&
+ 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?
@@ -8029,6 +8051,8 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
get_params(p, &kattr);
kattr.sched_flags &= SCHED_FLAG_ALL;

+ kattr.sched_latency_nice = p->latency_nice;
+
#ifdef CONFIG_UCLAMP_TASK
/*
* This could race with another potential updater, but this is fine
diff --git a/tools/include/uapi/linux/sched.h b/tools/include/uapi/linux/sched.h
index 3bac0a8ceab2..b2e932c25be6 100644
--- a/tools/include/uapi/linux/sched.h
+++ b/tools/include/uapi/linux/sched.h
@@ -132,6 +132,7 @@ 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_NICE 0x80

#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
SCHED_FLAG_KEEP_PARAMS)
@@ -143,6 +144,7 @@ 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_NICE)

#endif /* _UAPI_LINUX_SCHED_H */
--
2.17.1