Re: [PATCH v5 3/7] sched: Allow sched_{get,set}attr to change latency_nice of the task

From: K Prateek Nayak
Date: Wed Oct 12 2022 - 11:08:03 EST

Hello Vincent,

On 9/25/2022 8:09 PM, Vincent Guittot wrote:
> From: Parth Shah <parth@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> [rebase and add a dedicated __setscheduler_latency ]
> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> ---
> 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

[1]

>
> #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 ada2d05bd894..6a6116ea4c2c 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..ecc4884bfe4b 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

Small nit.
Can you change the "x" in "0X80" to lower case here to make it
consistent with [1] and other #define in the same file. When building
tools like perf, I see the following warning:

Warning: Kernel ABI header at 'tools/include/uapi/linux/sched.h' differs from latest version at 'include/uapi/linux/sched.h'
diff -u tools/include/uapi/linux/sched.h include/uapi/linux/sched.h

Following is the output of
diff -u tools/include/uapi/linux/sched.h include/uapi/linux/sched.h

--- tools/include/uapi/linux/sched.h 2022-10-12 14:56:00.925360275 +0000
+++ include/uapi/linux/sched.h 2022-10-12 14:56:00.917360219 +0000
@@ -132,7 +132,7 @@
#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_LATENCY_NICE 0x80

#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
SCHED_FLAG_KEEP_PARAMS)
--

>
> #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 */

--
Thanks and Regards,
Prateek