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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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