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    SubjectRe: [RFC][PATCH 4/8] sched: add smt_gain
    On Tue, Sep 01, 2009 at 10:34:35AM +0200, Peter Zijlstra wrote:
    > 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% */ \

    /* 15% of SCHED_LOAD_SCALE */ , I suppose.

    > }
    > #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;
    > }
    >
    > --

    --
    Thanks and Regards
    gautham


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