Messages in this thread | | | Date | Sun, 22 Oct 2006 02:16:19 -0700 | From | Paul Jackson <> | Subject | Re: [RFC] Cpuset: remove useless sched domain line |
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> > if (!is_cpu_exclusive(cur)) { > > - cpus_or(pspan, pspan, cur->cpus_allowed); > > if (cpus_equal(pspan, cur->cpus_allowed)) > > return; > > cspan = CPU_MASK_NONE; > > > I dont think this is a valid optimization. What we are checking here > is if a previously exclusive cpuset has been changed to a non-exclusive one > (echo 0 > cpu_exclusive), we then OR all the cpus in the current cpuset > to the parent cpuset. We then rebuild a sched domain to include all of the cpus > in the current cpuset and those in the parent not part of exclusive children
Not that it matters, but I don't think you need to OR in the current cpuset cpus to the parents cpus (pspan) here, because they are already in pspan.
Look at the surrounding code:
pspan = par->cpus_allowed; list_for_each_entry(c, &par->children, sibling) { if (is_cpu_exclusive(c)) cpus_andnot(pspan, pspan, c->cpus_allowed); } if (!is_cpu_exclusive(cur)) { cpus_or(pspan, pspan, cur->cpus_allowed); if (cpus_equal(pspan, cur->cpus_allowed)) return; cspan = CPU_MASK_NONE;
'pspan' starts out with all the parents cpus, which must be a superset of currents cpus (cur->cpus_allowed.)
Then we subtract (cpus_andnot) from pspan the cpus in the cpu_exclusive siblings of current. Since current is not cpu_exclusive, and since the cpus of its cpu_exclusive sibling cpusets cannot overlap with currents cpus, we could not have subtracted any current cpu from pspan.
So pspan is still a superset of currents cpus.
So OR'ing in currents cpus to pspan is a no-op.
-- I won't rest till it's the best ... Programmer, Linux Scalability Paul Jackson <pj@sgi.com> 1.925.600.0401 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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