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    Subject[RFC v4 5/6] sched/deadline: do not reclaim the whole CPU bandwidth
    Date
    From: Luca Abeni <luca.abeni@unitn.it>

    Original GRUB tends to reclaim 100% of the CPU time... And this
    allows a CPU hog to starve non-deadline tasks.
    To address this issue, allow the scheduler to reclaim only a
    specified fraction of CPU time.

    Signed-off-by: Luca Abeni <luca.abeni@unitn.it>
    ---
    kernel/sched/core.c | 4 ++++
    kernel/sched/deadline.c | 7 ++++++-
    kernel/sched/sched.h | 6 ++++++
    3 files changed, 16 insertions(+), 1 deletion(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 5030b3c..4010af7 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -8286,6 +8286,10 @@ static void sched_dl_do_global(void)
    raw_spin_unlock_irqrestore(&dl_b->lock, flags);

    rcu_read_unlock_sched();
    + if (dl_b->bw == -1)
    + cpu_rq(cpu)->dl.non_deadline_bw = 0;
    + else
    + cpu_rq(cpu)->dl.non_deadline_bw = (1 << 20) - new_bw;
    }
    }

    diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
    index 361887b..7585dfb 100644
    --- a/kernel/sched/deadline.c
    +++ b/kernel/sched/deadline.c
    @@ -151,6 +151,11 @@ void init_dl_rq(struct dl_rq *dl_rq)
    #else
    init_dl_bw(&dl_rq->dl_bw);
    #endif
    + if (global_rt_runtime() == RUNTIME_INF)
    + dl_rq->non_deadline_bw = 0;
    + else
    + dl_rq->non_deadline_bw = (1 << 20) -
    + to_ratio(global_rt_period(), global_rt_runtime());
    }

    #ifdef CONFIG_SMP
    @@ -773,7 +778,7 @@ extern bool sched_rt_bandwidth_account(struct rt_rq *rt_rq);
    */
    u64 grub_reclaim(u64 delta, struct rq *rq)
    {
    - return (delta * rq->dl.running_bw) >> 20;
    + return (delta * (rq->dl.non_deadline_bw + rq->dl.running_bw)) >> 20;
    }

    /*
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index e422803..ef4bdaa 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -542,6 +542,12 @@ struct dl_rq {
    * task blocks
    */
    u64 running_bw;
    +
    + /*
    + * Fraction of the CPU utilization that cannot be reclaimed
    + * by the GRUB algorithm.
    + */
    + u64 non_deadline_bw;
    };

    #ifdef CONFIG_SMP
    --
    2.7.4
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