Messages in this thread | | | Date | Mon, 4 Jun 2012 13:16:14 -0500 | From | Dimitri Sivanich <> | Subject | Re: relax_domain_level boot parameter has no effect |
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On Mon, Jun 04, 2012 at 05:37:42PM +0200, Peter Zijlstra wrote: > On Fri, 2012-06-01 at 16:03 -0500, Dimitri Sivanich wrote: > > I noticed (and verified) that the relax_domain_level boot parameter does not > > get processed because sched_domain_level_max is 0 at the time that > > setup_relax_domain_level() is run. > > > > int sched_domain_level_max; > > > > static int __init setup_relax_domain_level(char *str) > > { > > unsigned long val; > > > > val = simple_strtoul(str, NULL, 0); > > if (val < sched_domain_level_max) > > default_relax_domain_level = val; > > > > return 1; > > } > > __setup("relax_domain_level=", setup_relax_domain_level); > > Ah indeed.. this has been so for a while I guess.
On a very related note, the sched_relax_domain_level setting in cpuset doesn't appear to work correctly either (if I'm interpreting all of this correctly).
The reason is that the build_sched_domain() routine calls the set_domain_attribute() routine prior to setting the sd->level, however, the set_domain_attribute() routine relies on the sd->level to decide whether idle load balancing will be off/on.
static void set_domain_attribute(struct sched_domain *sd, .. ==> if (request < sd->level) { /* turn off idle balance on this domain */ .. .. struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl, .. ==> set_domain_attribute(sd, attr); cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu)); if (child) { ==> sd->level = child->level + 1; sched_domain_level_max = max(sched_domain_level_max, sd->level);
> What are you using this knob for?
I was poking around for different ways to turn off idle load balancing when I ran into all of this.
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