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    Subject[RFC][PATCH 2/8] sched: SD_PREFER_SIBLING
    Do the placement thing using SD flags

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/sched.h | 29 +++++++++++++++--------------
    kernel/sched.c | 14 +++++++++++++-
    2 files changed, 28 insertions(+), 15 deletions(-)

    Index: linux-2.6/include/linux/sched.h
    ===================================================================
    --- linux-2.6.orig/include/linux/sched.h
    +++ linux-2.6/include/linux/sched.h
    @@ -808,18 +808,19 @@ enum cpu_idle_type {
    #define SCHED_LOAD_SCALE_FUZZ SCHED_LOAD_SCALE

    #ifdef CONFIG_SMP
    -#define SD_LOAD_BALANCE 1 /* Do load balancing on this domain. */
    -#define SD_BALANCE_NEWIDLE 2 /* Balance when about to become idle */
    -#define SD_BALANCE_EXEC 4 /* Balance on exec */
    -#define SD_BALANCE_FORK 8 /* Balance on fork, clone */
    -#define SD_WAKE_IDLE 16 /* Wake to idle CPU on task wakeup */
    -#define SD_WAKE_AFFINE 32 /* Wake task to waking CPU */
    -#define SD_WAKE_BALANCE 64 /* Perform balancing at task wakeup */
    -#define SD_SHARE_CPUPOWER 128 /* Domain members share cpu power */
    -#define SD_POWERSAVINGS_BALANCE 256 /* Balance for power savings */
    -#define SD_SHARE_PKG_RESOURCES 512 /* Domain members share cpu pkg resources */
    -#define SD_SERIALIZE 1024 /* Only a single load balancing instance */
    -#define SD_WAKE_IDLE_FAR 2048 /* Gain latency sacrificing cache hit */
    +#define SD_LOAD_BALANCE 0x0001 /* Do load balancing on this domain. */
    +#define SD_BALANCE_NEWIDLE 0x0002 /* Balance when about to become idle */
    +#define SD_BALANCE_EXEC 0x0004 /* Balance on exec */
    +#define SD_BALANCE_FORK 0x0008 /* Balance on fork, clone */
    +#define SD_WAKE_IDLE 0x0010 /* Wake to idle CPU on task wakeup */
    +#define SD_WAKE_AFFINE 0x0020 /* Wake task to waking CPU */
    +#define SD_WAKE_BALANCE 0x0040 /* Perform balancing at task wakeup */
    +#define SD_SHARE_CPUPOWER 0x0080 /* Domain members share cpu power */
    +#define SD_POWERSAVINGS_BALANCE 0x0100 /* Balance for power savings */
    +#define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg resources */
    +#define SD_SERIALIZE 0x0400 /* Only a single load balancing instance */
    +#define SD_WAKE_IDLE_FAR 0x0800 /* Gain latency sacrificing cache hit */
    +#define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling domain */

    enum powersavings_balance_level {
    POWERSAVINGS_BALANCE_NONE = 0, /* No power saving load balance */
    @@ -839,7 +840,7 @@ static inline int sd_balance_for_mc_powe
    if (sched_smt_power_savings)
    return SD_POWERSAVINGS_BALANCE;

    - return 0;
    + return SD_PREFER_SIBLING;
    }

    static inline int sd_balance_for_package_power(void)
    @@ -847,7 +848,7 @@ static inline int sd_balance_for_package
    if (sched_mc_power_savings | sched_smt_power_savings)
    return SD_POWERSAVINGS_BALANCE;

    - return 0;
    + return SD_PREFER_SIBLING;
    }

    /*
    Index: linux-2.6/kernel/sched.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched.c
    +++ linux-2.6/kernel/sched.c
    @@ -3803,9 +3803,13 @@ static inline void update_sd_lb_stats(st
    const struct cpumask *cpus, int *balance,
    struct sd_lb_stats *sds)
    {
    + struct sched_domain *child = sd->child;
    struct sched_group *group = sd->groups;
    struct sg_lb_stats sgs;
    - int load_idx;
    + int load_idx, prefer_sibling = 0;
    +
    + if (child && child->flags & SD_PREFER_SIBLING)
    + prefer_sibling = 1;

    init_sd_power_savings_stats(sd, sds, idle);
    load_idx = get_sd_load_idx(sd, idle);
    @@ -3825,6 +3829,14 @@ static inline void update_sd_lb_stats(st
    sds->total_load += sgs.group_load;
    sds->total_pwr += group->__cpu_power;

    + /*
    + * In case the child domain prefers tasks go to siblings
    + * first, lower the group capacity to one so that we'll try
    + * and move all the excess tasks away.
    + */
    + if (prefer_sibling)
    + sgs.group_capacity = 1;
    +
    if (local_group) {
    sds->this_load = sgs.avg_load;
    sds->this = group;
    --



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