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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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