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@xxxxxxxxx>
Signed-off-by: Dinakar Guniguntala <dino@xxxxxxxxxx>
---
include/linux/sched.h | 1 +
include/linux/topology.h | 1 +
kernel/sched.c | 8 +++++++-
3 files changed, 9 insertions(+), 1 deletion(-)
Index: linux-2.6.31.4-rt14/include/linux/sched.h
===================================================================
--- linux-2.6.31.4-rt14.orig/include/linux/sched.h 2009-10-16 09:15:30.000000000 -0400
+++ linux-2.6.31.4-rt14/include/linux/sched.h 2009-10-16 09:15:34.000000000 -0400
@@ -966,6 +966,7 @@
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-2.6.31.4-rt14/include/linux/topology.h
===================================================================
--- linux-2.6.31.4-rt14.orig/include/linux/topology.h 2009-10-16 09:15:16.000000000 -0400
+++ linux-2.6.31.4-rt14/include/linux/topology.h 2009-10-16 09:15:34.000000000 -0400
@@ -99,6 +99,7 @@
| SD_SHARE_CPUPOWER, \
.last_balance = jiffies, \
.balance_interval = 1, \
+ .smt_gain = 1178, /* 15% */ \
}
#endif
#endif /* CONFIG_SCHED_SMT */
Index: linux-2.6.31.4-rt14/kernel/sched.c
===================================================================
--- linux-2.6.31.4-rt14.orig/kernel/sched.c 2009-10-16 09:15:32.000000000 -0400
+++ linux-2.6.31.4-rt14/kernel/sched.c 2009-10-16 09:15:34.000000000 -0400
@@ -8729,9 +8729,15 @@
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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