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    Subject[PATCH 7/9] numa,sched: do statistics calculation using local variables only
    Date
    From: Rik van Riel <riel@redhat.com>

    The current code in task_numa_placement calculates the difference
    between the old and the new value, but also temporarily stores half
    of the old value in the per-process variables.

    The NUMA balancing code looks at those per-process variables, and
    having other tasks temporarily see halved statistics could lead to
    unwanted numa migrations. This can be avoided by doing all the math
    in local variables.

    This change also simplifies the code a little.

    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Chegu Vinod <chegu_vinod@hp.com>
    Acked-by: Mel Gorman <mgorman@suse.de>
    Signed-off-by: Rik van Riel <riel@redhat.com>
    ---
    kernel/sched/fair.c | 12 ++++--------
    1 file changed, 4 insertions(+), 8 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index bd2100c..f713f3a 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -1518,12 +1518,9 @@ static void task_numa_placement(struct task_struct *p)
    long diff, f_diff, f_weight;

    i = task_faults_idx(nid, priv);
    - diff = -p->numa_faults_memory[i];
    - f_diff = -p->numa_faults_cpu[i];

    /* Decay existing window, copy faults since last scan */
    - p->numa_faults_memory[i] >>= 1;
    - p->numa_faults_memory[i] += p->numa_faults_buffer_memory[i];
    + diff = p->numa_faults_buffer_memory[i] - p->numa_faults_memory[i] / 2;
    fault_types[priv] += p->numa_faults_buffer_memory[i];
    p->numa_faults_buffer_memory[i] = 0;

    @@ -1537,13 +1534,12 @@ static void task_numa_placement(struct task_struct *p)
    f_weight = (16384 * runtime *
    p->numa_faults_buffer_cpu[i]) /
    (total_faults * period + 1);
    - p->numa_faults_cpu[i] >>= 1;
    - p->numa_faults_cpu[i] += f_weight;
    + f_diff = f_weight - p->numa_faults_cpu[i] / 2;
    p->numa_faults_buffer_cpu[i] = 0;

    + p->numa_faults_memory[i] += diff;
    + p->numa_faults_cpu[i] += f_diff;
    faults += p->numa_faults_memory[i];
    - diff += p->numa_faults_memory[i];
    - f_diff += p->numa_faults_cpu[i];
    p->total_numa_faults += diff;
    if (p->numa_group) {
    /* safe because we can only change our own group */
    --
    1.8.4.2


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