On Tue, Nov 12, 2013 at 10:11:26PM +0530, Srikar Dronamraju wrote: > After Commit-id 863bffc80898 (sched/fair: Fix group power_orig > computation), we might end up computing group power before the > sched_domain for a cpu is updated. > > Update with cpu_power, if rq->sd is not yet updated. > > Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com> > --- > Changelog since v1: Fix divide by zero errors that can result because > power/power_orig was set to 0.
Duh yes!, init_sched_groups_power() is called before we attach the actual domains, so the above will _always_ fail for the build_sched_domain() case. I was a bit puzzled how we could ever have 0 since surely at least the current cpu should have some !0 contribution, but no! --- Subject: sched: Check sched_domain before computing group power From: Srikar Dronamraju <sri...@linux.vnet.ibm.com> Date: Tue, 12 Nov 2013 22:11:26 +0530 After Commit-id 863bffc80898 (sched/fair: Fix group power_orig computation), we can dereference rq->sd before its set. Fix this by falling back to power_of() in this case and add a comment explaining things. Cc: mi...@neuling.org Cc: mi...@kernel.org Cc: h...@zytor.com Cc: t...@linutronix.de Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com> [peterz: added comment and tweaked patch] Signed-off-by: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/r/20131112164126.gf2...@linux.vnet.ibm.com --- kernel/sched/fair.c | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5354,10 +5354,31 @@ void update_group_power(struct sched_dom */ for_each_cpu(cpu, sched_group_cpus(sdg)) { - struct sched_group *sg = cpu_rq(cpu)->sd->groups; + struct sched_group_power *sgp; + struct rq *rq = cpu_rq(cpu); - power_orig += sg->sgp->power_orig; - power += sg->sgp->power; + /* + * build_sched_domains() -> init_sched_groups_power() + * gets here before we've attached the domains to the + * runqueues. + * + * Use power_of(), which is set irrespective of domains + * in update_cpu_power(). + * + * This avoids power/power_orig from being 0 and + * causing divide-by-zero issues on boot. + * + * Runtime updates will correct power_orig. + */ + if (!rq->sd) { + power_orig += power_of(cpu); + power += power_of(cpu); + continue; + } + + sgp = rq->sd->groups->sgp; + power_orig += sgp->power_orig; + power += sgp->power; } } else { /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
