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sched: Add smt_gain

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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>
Tested-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Gautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.073345955@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-09-01 10:34:35 +02:00 committed by Ingo Molnar
parent cc9fba7d76
commit a52bfd7358
3 changed files with 9 additions and 1 deletions
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1
include/linux/sched.h
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@ -921,6 +921,7 @@ 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;

1
include/linux/topology.h
View file

@ -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 */

8
kernel/sched.c
View file

@ -8523,9 +8523,15 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd)
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;
}