Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [PATCH] cpuset and sched domains: sched_load_balance flag | Date | Wed, 3 Oct 2007 05:25:29 +1000 |
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On Wednesday 03 October 2007 21:38, Paul Jackson wrote: > > OK, so to really do anything different (from a non-partitioned setup), > > you would need to set sched_load_balance=0 for the root cpuset?
> > Suppose you do that to hard partition the machine, what happens to > > newly created tasks like kernel threads or things that aren't in a > > cpuset? > > Well ... --every-- task is in a cpuset, always. Newly created tasks > start in the cpuset of their parent. Grep for 'the_top_cpuset_hack' > in kernel/cpuset.c to see the lengths to which we go to ensure that > current->cpuset always resolves somewhere.
OK, then non-balancing cpuset.
> The usual case on the big systems that I care about the most is > that we move (almost) every task out of the top cpuset, into smaller > cpusets, because we don't want some random thread intruding on the > CPUs dedicated to a particular job. The only threads left in the root > cpuset are pinned kernel threads, such as for thread migration, per-cpu > irq handlers and various per-cpu and per-node disk and file flushers > and such. These threads aren't going anywhere, regardless. But no > thread that is willing to run anywhere is left free to run anywhere.
These are what I'm worried about, and things like kswapd, pdflush, could definitely use a huge amount of CPU.
If you are interested in hard partitioning the system, you most definitely want these things to be balanced across the non-isolated CPUs.
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