From: Vaidyanathan Srinivasan Date: Wed, 30 Oct 2013 03:12:42 +0000 (+0530) Subject: sched: Fix asymmetric scheduling for POWER7 X-Git-Tag: firefly_0821_release~176^2~5035^2~3 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=2042abe7977222ef606306faa2dce8fd51e98e65;p=firefly-linux-kernel-4.4.55.git sched: Fix asymmetric scheduling for POWER7 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 Signed-off-by: Vaidyanathan Srinivasan Signed-off-by: Preeti U Murthy Tested-by: Michael Neuling Signed-off-by: Peter Zijlstra Cc: vincent.guittot@linaro.org Cc: bitbucket@online.de Cc: benh@kernel.crashing.org Cc: anton@samba.org Cc: Morten.Rasmussen@arm.com Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131030031242.23426.13019.stgit@preeti.in.ibm.com Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 41c02b6b090e..074551a792f7 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6800,7 +6800,7 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1) goto need_kick_unlock; - if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight + if (sd->flags & SD_ASYM_PACKING && (cpumask_first_and(nohz.idle_cpus_mask, sched_domain_span(sd)) < cpu)) goto need_kick_unlock;