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>
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>

3 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 651dded25720..9c81c921acb3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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;
 
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 7402c1a27c4f..6203ae5067ce 100644
--- a/include/linux/topology.h
+++ b/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 */
diff --git a/kernel/sched.c b/kernel/sched.c
index ecb4a47d4214..55112261027b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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;
         }