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    SubjectRe: [Lse-tech] [PATCH] cpusets - big numa cpu and memory placement
    Matthew Dobson wrote:
    > On Fri, 2004-10-08 at 17:18, Nick Piggin wrote:
    >>Matthew Dobson wrote:
    >>>I think this example is easily achievable with the sched_domains
    >>>modifications I am proposing. You can still create your 128 CPU
    >>>exclusive domain, called big_domain (due to my lack of naming
    >>>creativity), and further divide big_domain into smaller, non-exclusive
    >>>sched_domains. We do this all the time, albeit statically at boot time,
    >>>with the current sched_domains code. When we create a 4-node domain on
    >>>IA64, and underneath it we create 4 1-node domains. We've now
    >>>partitioned the system into 4 sched_domains, each containing 4 cpus.
    >>>Balancing between these 4 node-level sched_domains is allowed, but can
    >>>be disallowed by not setting the SD_LOAD_BALANCE flag. Your example
    >>>does show that it can be more than just a convenient way to group tasks,
    >>>but your example can be done with what I'm proposing.
    >>You wouldn't be able to do this just with sched domains, because
    >>it doesn't know anything about individual tasks. As soon as you
    >>have some overlap, all your tasks can escape out of your domain.
    >>I don't think there is a really nice way to do overlapping sets.
    >>Those that want them need to just use cpu affinity for now.
    > Well, the tasks can escape out of the domain iff you have the
    > SD_LOAD_BALANCE flag set on that domain. If SD_LOAD_BALANCE isn't set,
    > then when the scheduler tick goes off, and the code looks at the domain,
    > it will see the lack of the flag and will not attempt to balance the
    > domain, correct? This is what we currently do with the 'isolated'
    > domains, right?

    Yeah that's right. Well you have to remove some of the other SD_
    flags as well (eg. SD_BALANCE_EXEC, SD_WAKE_BALANCE).

    But I don't think there is much point in overlapping sets which
    don't do any balancing. They might as well not exist at all.

    > You're right that you can get some of the more obscure semantics of the
    > various flavors of cpusets by leveraging sched_domains AND
    > cpus_allowed. I don't have any desire to remove that ability, just keep
    > it as the exception.

    I think at this stage, overlapping cpu sets are the exception. It
    is pretty logical that they're going to require some per-task info,
    because the balancer can't otherwise differentiate between two tasks
    on the same runqueue but in different cpu sets.

    sched-domains gives you a nice clean way to do exclusive partitioning,
    and I can't imagine it would be too common to want to do overlapping
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