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    Subject[RFC][PATCH 04/14] sched: add smt_gain
    The idea is that multi-threading a core yields more work capacity than
    a single thread, provide a way to express a static gain for threads.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/sched.h | 1 +
    include/linux/topology.h | 1 +
    kernel/sched.c | 8 +++++++-
    3 files changed, 9 insertions(+), 1 deletion(-)
    Index: linux-2.6/include/linux/sched.h
    ===================================================================
    --- linux-2.6.orig/include/linux/sched.h
    +++ linux-2.6/include/linux/sched.h
    @@ -930,6 +930,7 @@ struct sched_domain {
    unsigned int newidle_idx;
    unsigned int wake_idx;
    unsigned int forkexec_idx;
    + unsigned int smt_gain;
    int flags; /* See SD_* */
    enum sched_domain_level level;

    Index: linux-2.6/include/linux/topology.h
    ===================================================================
    --- linux-2.6.orig/include/linux/topology.h
    +++ linux-2.6/include/linux/topology.h
    @@ -99,6 +99,7 @@ int arch_update_cpu_topology(void);
    | SD_SHARE_CPUPOWER, \
    .last_balance = jiffies, \
    .balance_interval = 1, \
    + .smt_gain = 1178, /* 15% */ \
    }
    #endif
    #endif /* CONFIG_SCHED_SMT */
    Index: linux-2.6/kernel/sched.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched.c
    +++ linux-2.6/kernel/sched.c
    @@ -8490,9 +8490,15 @@ static void init_sched_groups_power(int
    weight = cpumask_weight(sched_domain_span(sd));
    /*
    * SMT siblings share the power of a single core.
    + * Usually multiple threads get a better yield out of
    + * that one core than a single thread would have,
    + * reflect that in sd->smt_gain.
    */
    - if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1)
    + if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
    + power *= sd->smt_gain;
    power /= weight;
    + power >>= SCHED_LOAD_SHIFT;
    + }
    sg_inc_cpu_power(sd->groups, power);
    return;
    }
    --



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