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    Subject[PATCH v4 5/8] sched: Enable sched_feat callbacks on enable/disable
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    When a scheduler feature is enabled or disabled, the sched_feat_enable()
    and sched_feat_disable() functions are invoked respectively for that
    feature. For features that don't require resetting any state, this works
    fine. However, there will be an upcoming feature called SHARED_RUNQ
    which needs to drain all tasks from a set of global shared runqueues in
    order to avoid stale tasks from staying in the queues after the feature
    has been disabled.

    This patch therefore defines a new SCHED_FEAT_CALLBACK macro which
    allows scheduler features to specify a callback that should be invoked
    when a feature is enabled or disabled respectively. The SCHED_FEAT macro
    assumes a NULL callback.

    Signed-off-by: David Vernet <void@manifault.com>
    ---
    kernel/sched/core.c | 4 ++--
    kernel/sched/debug.c | 18 ++++++++++++++----
    kernel/sched/sched.h | 16 ++++++++++------
    3 files changed, 26 insertions(+), 12 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 9ad7f0255e14..045ac2539f37 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -124,12 +124,12 @@ DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
    * sysctl_sched_features, defined in sched.h, to allow constants propagation
    * at compile time and compiler optimization based on features default.
    */
    -#define SCHED_FEAT(name, enabled) \
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) \
    (1UL << __SCHED_FEAT_##name) * enabled |
    const_debug unsigned int sysctl_sched_features =
    #include "features.h"
    0;
    -#undef SCHED_FEAT
    +#undef SCHED_FEAT_CALLBACK

    /*
    * Print a warning if need_resched is set for the given duration (if
    diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
    index 168eecc209b4..0b72799c7e84 100644
    --- a/kernel/sched/debug.c
    +++ b/kernel/sched/debug.c
    @@ -44,14 +44,14 @@ static unsigned long nsec_low(unsigned long long nsec)

    #define SPLIT_NS(x) nsec_high(x), nsec_low(x)

    -#define SCHED_FEAT(name, enabled) \
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) \
    #name ,

    static const char * const sched_feat_names[] = {
    #include "features.h"
    };

    -#undef SCHED_FEAT
    +#undef SCHED_FEAT_CALLBACK

    static int sched_feat_show(struct seq_file *m, void *v)
    {
    @@ -72,22 +72,32 @@ static int sched_feat_show(struct seq_file *m, void *v)
    #define jump_label_key__true STATIC_KEY_INIT_TRUE
    #define jump_label_key__false STATIC_KEY_INIT_FALSE

    -#define SCHED_FEAT(name, enabled) \
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) \
    jump_label_key__##enabled ,

    struct static_key sched_feat_keys[__SCHED_FEAT_NR] = {
    #include "features.h"
    };

    -#undef SCHED_FEAT
    +#undef SCHED_FEAT_CALLBACK
    +
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) cb,
    +static const sched_feat_change_f sched_feat_cbs[__SCHED_FEAT_NR] = {
    +#include "features.h"
    +};
    +#undef SCHED_FEAT_CALLBACK

    static void sched_feat_disable(int i)
    {
    + if (sched_feat_cbs[i])
    + sched_feat_cbs[i](false);
    static_key_disable_cpuslocked(&sched_feat_keys[i]);
    }

    static void sched_feat_enable(int i)
    {
    + if (sched_feat_cbs[i])
    + sched_feat_cbs[i](true);
    static_key_enable_cpuslocked(&sched_feat_keys[i]);
    }
    #else
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index 53fe2294eec7..517e67a0cc9a 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -2091,6 +2091,8 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
    #endif
    }

    +#define SCHED_FEAT(name, enabled) SCHED_FEAT_CALLBACK(name, enabled, NULL)
    +
    /*
    * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
    */
    @@ -2100,7 +2102,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
    # define const_debug const
    #endif

    -#define SCHED_FEAT(name, enabled) \
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) \
    __SCHED_FEAT_##name ,

    enum {
    @@ -2108,7 +2110,7 @@ enum {
    __SCHED_FEAT_NR,
    };

    -#undef SCHED_FEAT
    +#undef SCHED_FEAT_CALLBACK

    #ifdef CONFIG_SCHED_DEBUG

    @@ -2119,14 +2121,14 @@ enum {
    extern const_debug unsigned int sysctl_sched_features;

    #ifdef CONFIG_JUMP_LABEL
    -#define SCHED_FEAT(name, enabled) \
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) \
    static __always_inline bool static_branch_##name(struct static_key *key) \
    { \
    return static_key_##enabled(key); \
    }

    #include "features.h"
    -#undef SCHED_FEAT
    +#undef SCHED_FEAT_CALLBACK

    extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
    #define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
    @@ -2144,17 +2146,19 @@ extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
    * constants propagation at compile time and compiler optimization based on
    * features default.
    */
    -#define SCHED_FEAT(name, enabled) \
    +#define SCHED_FEAT_CALLBACK(name, enabled, cb) \
    (1UL << __SCHED_FEAT_##name) * enabled |
    static const_debug __maybe_unused unsigned int sysctl_sched_features =
    #include "features.h"
    0;
    -#undef SCHED_FEAT
    +#undef SCHED_FEAT_CALLBACK

    #define sched_feat(x) !!(sysctl_sched_features & (1UL << __SCHED_FEAT_##x))

    #endif /* SCHED_DEBUG */

    +typedef void (*sched_feat_change_f)(bool enabling);
    +
    extern struct static_key_false sched_numa_balancing;
    extern struct static_key_false sched_schedstats;

    --
    2.42.1
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