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    Subject[tip:sched/core] sched/core: Store maximum per-CPU capacity in root domain
    Commit-ID:  cd92bfd3b8cb0ec2ee825e55a3aee704cd55aea9
    Gitweb: http://git.kernel.org/tip/cd92bfd3b8cb0ec2ee825e55a3aee704cd55aea9
    Author: Dietmar Eggemann <dietmar.eggemann@arm.com>
    AuthorDate: Mon, 1 Aug 2016 19:53:35 +0100
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 18 Aug 2016 11:26:55 +0200

    sched/core: Store maximum per-CPU capacity in root domain

    To be able to compare the capacity of the target CPU with the highest
    available CPU capacity, store the maximum per-CPU capacity in the root
    domain.

    The max per-CPU capacity should be 1024 for all systems except SMT,
    where the capacity is currently based on smt_gain and the number of
    hardware threads and is <1024. If SMT can be brought to work with a
    per-thread capacity of 1024, this patch can be dropped and replaced by a
    hard-coded max capacity of 1024 (=SCHED_CAPACITY_SCALE).

    Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
    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: Mike Galbraith <efault@gmx.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: freedom.tan@mediatek.com
    Cc: keita.kobayashi.ym@renesas.com
    Cc: mgalbraith@suse.de
    Cc: sgurrappadi@nvidia.com
    Cc: vincent.guittot@linaro.org
    Cc: yuyang.du@intel.com
    Link: http://lkml.kernel.org/r/26c69258-9947-f830-a53e-0c54e7750646@arm.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/sched/core.c | 12 ++++++++++++
    kernel/sched/sched.h | 2 ++
    2 files changed, 14 insertions(+)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 4695df6..6924314 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -6903,6 +6903,7 @@ static int build_sched_domains(const struct cpumask *cpu_map,
    enum s_alloc alloc_state;
    struct sched_domain *sd;
    struct s_data d;
    + struct rq *rq = NULL;
    int i, ret = -ENOMEM;

    alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
    @@ -6953,11 +6954,22 @@ static int build_sched_domains(const struct cpumask *cpu_map,
    /* Attach the domains */
    rcu_read_lock();
    for_each_cpu(i, cpu_map) {
    + rq = cpu_rq(i);
    sd = *per_cpu_ptr(d.sd, i);
    +
    + /* Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing: */
    + if (rq->cpu_capacity_orig > READ_ONCE(d.rd->max_cpu_capacity))
    + WRITE_ONCE(d.rd->max_cpu_capacity, rq->cpu_capacity_orig);
    +
    cpu_attach_domain(sd, d.rd, i);
    }
    rcu_read_unlock();

    + if (rq) {
    + pr_info("span: %*pbl (max cpu_capacity = %lu)\n",
    + cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
    + }
    +
    ret = 0;
    error:
    __free_domain_allocs(&d, alloc_state, cpu_map);
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index afe76d0..420c05d 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -565,6 +565,8 @@ struct root_domain {
    */
    cpumask_var_t rto_mask;
    struct cpupri cpupri;
    +
    + unsigned long max_cpu_capacity;
    };

    extern struct root_domain def_root_domain;
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