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    Subject[PATCH v5 3/4] sched: Allow sched_{get,set}attr to change latency_nice of the task
    Date
    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>
    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 | 18 ++++++++++++++++++
    tools/include/uapi/linux/sched.h | 4 +++-
    4 files changed, 43 insertions(+), 2 deletions(-)

    diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
    index 2e3bc22c6f20..8778c51c7953 100644
    --- a/include/uapi/linux/sched.h
    +++ b/include/uapi/linux/sched.h
    @@ -127,6 +127,7 @@ 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)
    @@ -138,6 +139,7 @@ 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 c852153ddb0d..626ab61c1145 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.
    @@ -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_nice task's latency_nice value
    + *
    + * The latency_nice of a task can have any value in a range of
    + * [LATENCY_NICE_MIN..LATENCY_NICE_MAX].
    + *
    + * A task with latency_nice with the value of LATENCY_NICE_MIN can be
    + * taken for a task with lower latency requirements as opposed to the task with
    + * higher latency_nice.
    */
    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_nice;
    };

    #endif /* _UAPI_LINUX_SCHED_TYPES_H */
    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 866ea3d2d284..cd1fb9c8be26 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -4710,6 +4710,9 @@ 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);
    +
    + if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE)
    + p->latency_nice = attr->sched_latency_nice;
    }

    /* Actually do priority change: must hold pi & rq lock. */
    @@ -4867,6 +4870,13 @@ 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();

    @@ -4901,6 +4911,9 @@ 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;
    @@ -5149,6 +5162,9 @@ 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?
    @@ -5378,6 +5394,8 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
    else
    kattr.sched_nice = task_nice(p);

    + kattr.sched_latency_nice = p->latency_nice;
    +
    #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 2e3bc22c6f20..94adc87df0e6 100644
    --- a/tools/include/uapi/linux/sched.h
    +++ b/tools/include/uapi/linux/sched.h
    @@ -127,6 +127,7 @@ 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)
    @@ -138,6 +139,7 @@ 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 */
    --
    2.17.2
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