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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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