Re: [RFC] cpuset: add interface to isolated cpus

From: Nick Piggin
Date: Sat Oct 21 2006 - 06:53:34 EST


Paul Jackson wrote:
If you always have other domains overlapping them (regardless
that it is a parent), then what actual use does cpu_exclusive
flag have?


Good question. To be a tad too honest, I don't consider it to be
all that essential.

It does turn out to be a bit useful, in that you can be confident that
if you are administering the batch scheduler and it has a cpu_exclusive
cpuset covering a big chunk of your system, then no other cpuset other
than the top cpuset right above, which you administer pretty tightly,
could have anything overlapping it. You don't have to actually look
at the cpumasks in all the parallel cpusets and cross check each one
against the batch schedulers set of cpus for overlap.

But as you can see by grep'ing in kernel/cpuset.c, it is only used
to generate a couple of error returns, for things that you can do
just fine by turning off the cpu_exclusive flag.

Well, it was supposed to be used for sched-domains partitioning, and
its uselessness for anything else I guess is what threw me.

But even the way cpu_exclusive semantics are defined makes it not
quite compatible with partitioning anyway, unfortunately.

--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com -
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/