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    Subject[tip:sched/core] sched/topology: Add static_key for asymmetric CPU capacity optimizations
    Commit-ID:  df054e8445a4011e3d693c2268129c0456108663
    Gitweb: https://git.kernel.org/tip/df054e8445a4011e3d693c2268129c0456108663
    Author: Morten Rasmussen <morten.rasmussen@arm.com>
    AuthorDate: Wed, 4 Jul 2018 11:17:39 +0100
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 10 Sep 2018 11:05:48 +0200

    sched/topology: Add static_key for asymmetric CPU capacity optimizations

    The existing asymmetric CPU capacity code should cause minimal overhead
    for others. Putting it behind a static_key, it has been done for SMT
    optimizations, would make it easier to extend and improve without
    causing harm to others moving forward.

    Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: dietmar.eggemann@arm.com
    Cc: gaku.inami.xh@renesas.com
    Cc: valentin.schneider@arm.com
    Cc: vincent.guittot@linaro.org
    Link: http://lkml.kernel.org/r/1530699470-29808-2-git-send-email-morten.rasmussen@arm.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/sched/fair.c | 3 +++
    kernel/sched/sched.h | 1 +
    kernel/sched/topology.c | 9 ++++++++-
    3 files changed, 12 insertions(+), 1 deletion(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index f808ddf2a868..3e5071aeb117 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -6188,6 +6188,9 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
    {
    long min_cap, max_cap;

    + if (!static_branch_unlikely(&sched_asym_cpucapacity))
    + return 0;
    +
    min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
    max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;

    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index 4a2e8cae63c4..0f36adc31ba5 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -1185,6 +1185,7 @@ DECLARE_PER_CPU(int, sd_llc_id);
    DECLARE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
    DECLARE_PER_CPU(struct sched_domain *, sd_numa);
    DECLARE_PER_CPU(struct sched_domain *, sd_asym);
    +extern struct static_key_false sched_asym_cpucapacity;

    struct sched_group_capacity {
    atomic_t ref;
    diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
    index 5c4d583d53ee..b0cdf5e95bda 100644
    --- a/kernel/sched/topology.c
    +++ b/kernel/sched/topology.c
    @@ -398,6 +398,7 @@ DEFINE_PER_CPU(int, sd_llc_id);
    DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
    DEFINE_PER_CPU(struct sched_domain *, sd_numa);
    DEFINE_PER_CPU(struct sched_domain *, sd_asym);
    +DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);

    static void update_top_cache_domain(int cpu)
    {
    @@ -1705,6 +1706,7 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
    struct rq *rq = NULL;
    int i, ret = -ENOMEM;
    struct sched_domain_topology_level *tl_asym;
    + bool has_asym = false;

    alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
    if (alloc_state != sa_rootdomain)
    @@ -1720,8 +1722,10 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
    for_each_sd_topology(tl) {
    int dflags = 0;

    - if (tl == tl_asym)
    + if (tl == tl_asym) {
    dflags |= SD_ASYM_CPUCAPACITY;
    + has_asym = true;
    + }

    sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i);

    @@ -1773,6 +1777,9 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
    }
    rcu_read_unlock();

    + if (has_asym)
    + static_branch_enable_cpuslocked(&sched_asym_cpucapacity);
    +
    if (rq && sched_debug_enabled) {
    pr_info("root domain span: %*pbl (max cpu_capacity = %lu)\n",
    cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
    \
     
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