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From: Michael Neuling on 9 Apr 2010 02:30
When calculating capacity we use the following calculation:

capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);

In SMT2, power will be 1178/2 (provided we are not scaling power with
freq say) and SCHED_LOAD_SCALE will be 1024, resulting in capacity
being 1.

With SMT4 however, power will be 1178/4, hence capacity will end up as
0.

Fix this by ensuring capacity is always at least 1 after this
calculation.

Signed-off-by: Michael Neuling <mikey(a)neuling.org>
---
I'm not sure this is the correct fix but this works for me.
Original post here:
http://lkml.org/lkml/2010/3/30/884

---

kernel/sched_fair.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-2.6-ozlabs/kernel/sched_fair.c
===================================================================
--- linux-2.6-ozlabs.orig/kernel/sched_fair.c
+++ linux-2.6-ozlabs/kernel/sched_fair.c
@@ -1482,6 +1482,7 @@ static int select_task_rq_fair(struct ta
}

capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
+ capacity = max(capacity, 1UL);

if (tmp->flags & SD_POWERSAVINGS_BALANCE)
nr_running /= 2;
@@ -2488,6 +2489,7 @@ static inline void update_sg_lb_stats(st

sgs->group_capacity =
DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
+ sgs->group_capacity = max(sgs->group_capacity, 1UL);
}

/**
@@ -2795,9 +2797,11 @@ find_busiest_queue(struct sched_group *g

for_each_cpu(i, sched_group_cpus(group)) {
unsigned long power = power_of(i);
- unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
+ unsigned long capacity;
unsigned long wl;

+ capacity = max(DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE), 1UL);
+
if (!cpumask_test_cpu(i, cpus))
continue;

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