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    Subject[tip:sched/urgent] sched_rt: don't allocate cpumask in fastpath
    Commit-ID:  13b8bd0a5713bdf05659019badd7c0407984ece1
    Gitweb: http://git.kernel.org/tip/13b8bd0a5713bdf05659019badd7c0407984ece1
    Author: Rusty Russell <rusty@rustcorp.com.au>
    AuthorDate: Wed, 25 Mar 2009 15:01:22 +1030
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 1 Apr 2009 13:24:51 +0200

    sched_rt: don't allocate cpumask in fastpath

    Impact: cleanup

    As pointed out by Steven Rostedt. Since the arg in question is
    unused, we simply change cpupri_find() to accept NULL.

    Reported-by: Steven Rostedt <srostedt@redhat.com>
    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    LKML-Reference: <200903251501.22664.rusty@rustcorp.com.au>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    kernel/sched_cpupri.c | 5 +++--
    kernel/sched_rt.c | 15 ++++-----------
    2 files changed, 7 insertions(+), 13 deletions(-)

    diff --git a/kernel/sched_cpupri.c b/kernel/sched_cpupri.c
    index 1e00bfa..cdd3c89 100644
    --- a/kernel/sched_cpupri.c
    +++ b/kernel/sched_cpupri.c
    @@ -55,7 +55,7 @@ static int convert_prio(int prio)
    * cpupri_find - find the best (lowest-pri) CPU in the system
    * @cp: The cpupri context
    * @p: The task
    - * @lowest_mask: A mask to fill in with selected CPUs
    + * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
    *
    * Note: This function returns the recommended CPUs as calculated during the
    * current invokation. By the time the call returns, the CPUs may have in
    @@ -81,7 +81,8 @@ int cpupri_find(struct cpupri *cp, struct task_struct *p,
    if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
    continue;

    - cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
    + if (lowest_mask)
    + cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
    return 1;
    }

    diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
    index bac1061..fbec5a5 100644
    --- a/kernel/sched_rt.c
    +++ b/kernel/sched_rt.c
    @@ -805,20 +805,15 @@ static int select_task_rq_rt(struct task_struct *p, int sync)

    static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
    {
    - cpumask_var_t mask;
    -
    if (rq->curr->rt.nr_cpus_allowed == 1)
    return;

    - if (!alloc_cpumask_var(&mask, GFP_ATOMIC))
    - return;
    -
    if (p->rt.nr_cpus_allowed != 1
    - && cpupri_find(&rq->rd->cpupri, p, mask))
    - goto free;
    + && cpupri_find(&rq->rd->cpupri, p, NULL))
    + return;

    - if (!cpupri_find(&rq->rd->cpupri, rq->curr, mask))
    - goto free;
    + if (!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
    + return;

    /*
    * There appears to be other cpus that can accept
    @@ -827,8 +822,6 @@ static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
    */
    requeue_task_rt(rq, p, 1);
    resched_task(rq->curr);
    -free:
    - free_cpumask_var(mask);
    }

    #endif /* CONFIG_SMP */

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