Messages in this thread Patch in this message | | | Subject | [PATCH 2/3] sched: Fix asymmetric scheduling for POWER7 | From | Vaidyanathan Srinivasan <> | Date | Mon, 21 Oct 2013 17:14:52 +0530 |
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Asymmetric scheduling within a core is a scheduler loadbalancing feature that is triggered when SD_ASYM_PACKING flag is set. The goal for the load balancer is to move tasks to lower order idle SMT threads within a core on a POWER7 system.
In nohz_kick_needed(), we intend to check if our sched domain (core) is completely busy or we have idle cpu.
The following check for SD_ASYM_PACKING:
(cpumask_first_and(nohz.idle_cpus_mask, sched_domain_span(sd)) < cpu)
already covers the case of checking if the domain has an idle cpu, because cpumask_first_and() will not yield any set bits if this domain has no idle cpu.
Hence, nr_busy check against group weight can be removed.
Reported-by: Michael Neuling <michael.neuling@au1.ibm.com> Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> --- kernel/sched/fair.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 12f0eab..828ed97 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5821,8 +5821,8 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) goto need_kick_unlock; } - if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight - && (cpumask_first_and(nohz.idle_cpus_mask, + if (sd->flags & SD_ASYM_PACKING && + (cpumask_first_and(nohz.idle_cpus_mask, sched_domain_span(sd)) < cpu)) goto need_kick_unlock;
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