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    Subject[patch repost] sched: Fix group_capacity for sched_smt_powersavings=1
    Hi Peter,

    This is repost of the same patch

    After applying Suresh's fixes from discussion thread, we still need the attached patch
    to restore sched_smt_powersavings=1 functionality where tasks prefer
    sibling threads and keep more cores idle.

    Please apply to sched-tip, the patch is rebased and tested on today's
    sched-tip master.

    The attached patch will run 4 while(1) loops in two cores when
    sched_smt_power_savings=1. Tested on two socket, quad core, hyper
    threaded system.

    Additional testing was done on POWER platform where
    sched_smt_powersavings was able to consolidate tasks on sibling
    threads leaving more idle cores.

    sched: Fix group_capacity for sched_smt_powersavings=1

    sched_smt_powersavings for threaded systems need this fix for
    consolidation to sibling threads to work. Since threads have
    fractional capacity, group_capacity will turn out to be one
    always and not accommodate another task in the sibling thread.

    This fix makes group_capacity a function of cpumask_weight that
    will enable the power saving load balancer to pack tasks among
    sibling threads and keep more cores idle.

    Signed-off-by: Vaidyanathan Srinivasan <>

    diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
    index 5a5ea2c..7c0a29a 100644
    --- a/kernel/sched_fair.c
    +++ b/kernel/sched_fair.c
    @@ -2538,6 +2538,21 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
    if (prefer_sibling)
    sgs.group_capacity = min(sgs.group_capacity, 1UL);
    + /*
    + * If power savings balance is set at this domain, then
    + * make capacity equal to number of hardware threads to
    + * accommodate more tasks until capacity is reached.
    + */
    + else if (sd->flags & SD_POWERSAVINGS_BALANCE)
    + sgs.group_capacity =
    + cpumask_weight(sched_group_cpus(group));
    + /*
    + * The default group_capacity is rounded from sum of
    + * fractional cpu_powers of sibling hardware threads
    + * in order to enable fair use of available hardware
    + * resources.
    + */

    if (local_group) {
    sds->this_load = sgs.avg_load;
    @@ -2863,7 +2878,8 @@ static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle)
    !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
    return 0;

    - if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
    + if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP &&
    + sched_smt_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
    return 0;

     \ /
      Last update: 2010-03-22 17:37    [W:0.023 / U:2.104 seconds]
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