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    Subject[PATCH v4 05/12] sched/fair: Keep a fully_busy SMT sched group as busiest
    Date
    When comparing two fully_busy scheduling groups, keep the current busiest
    group if it represents an SMT core. Tasks in such scheduling group share
    CPU resources and need more help than tasks in a non-SMT fully_busy group.

    Cc: Ben Segall <bsegall@google.com>
    Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
    Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
    Cc: Ionela Voinescu <ionela.voinescu@arm.com>
    Cc: Len Brown <len.brown@intel.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Tim C. Chen <tim.c.chen@intel.com>
    Cc: Valentin Schneider <vschneid@redhat.com>
    Cc: x86@kernel.org
    Cc: linux-kernel@vger.kernel.org
    Tested-by: Zhang Rui <rui.zhang@intel.com>
    Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    ---
    Changes since v3:
    * None

    Changes since v2:
    * Introduced this patch.

    Changes since v1:
    * N/A
    ---
    kernel/sched/fair.c | 16 ++++++++++++++--
    1 file changed, 14 insertions(+), 2 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index b151e93ec316..ea23a5163bfa 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -9566,10 +9566,22 @@ static bool update_sd_pick_busiest(struct lb_env *env,
    * contention when accessing shared HW resources.
    *
    * XXX for now avg_load is not computed and always 0 so we
    - * select the 1st one.
    + * select the 1st one, except if @sg is composed of SMT
    + * siblings.
    */
    - if (sgs->avg_load <= busiest->avg_load)
    +
    + if (sgs->avg_load < busiest->avg_load)
    return false;
    +
    + if (sgs->avg_load == busiest->avg_load) {
    + /*
    + * SMT sched groups need more help than non-SMT groups.
    + * If @sg happens to also be SMT, either choice is good.
    + */
    + if (sds->busiest->flags & SD_SHARE_CPUCAPACITY)
    + return false;
    + }
    +
    break;

    case group_has_spare:
    --
    2.25.1
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