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    SubjectRe: [-mm] Add an owner to the mm_struct (v8)
    On Sat, Apr 5, 2008 at 10:48 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > Paul Menage wrote:
    > > On Sat, Apr 5, 2008 at 7:47 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > >> Repeating my question earlier
    > >>
    > >> Can we delay setting task->cgroups = &init_css_set for the group_leader, until
    > >> all threads have exited?
    > >
    > > Potentially, yes. It also might make more sense to move the
    > > exit_cgroup() for all threads to a later point rather than special
    > > case delayed group leaders.
    > >
    >
    > Yes, that makes sense. I think that patch should be independent of this one
    > though? What do you think?

    Yes, it would probably need to be a separate patch. The current
    positioning of cgroup_exit() is more or less inherited from cpusets.
    I'd need to figure out if a change like that would break anything.

    > >
    > > Yes, I agree it could potentially happen. But it seems like a strange
    > > thing to do if you're planning to be not have the same groupings for
    > > cpu and va.
    >
    > It's easier to set it up that way. Usually the end user gets the same SLA for
    > memory, CPU and other resources, so it makes sense to bind the controllers together.
    >

    True - but in that case why wouldn't they have the same SLA for
    virtual address space too?

    >
    > >> I measured the overhead of removing the delay_group_leader optimization and
    > >> found a 4% impact on throughput (with volanomark, that is one of the
    > >> multi-threaded benchmarks I know of).
    > >
    > > Interesting, I thought (although I've never actually looked at the
    > > code) that volanomark was more of a scheduling benchmark than a
    > > process start/exit benchmark. How frequently does it have processes
    > > (not threads) exiting?
    > >
    >
    > I could not find any other interesting benchmark for benchmarking fork/exits. I
    > know that volanomark is heavily threaded, so I used it. The threads quickly exit
    > after processing the messages, I thought that would be a good test to see the
    > overhead.

    But surely the performance of thread exits wouldn't be affected by the
    delay_group_leader(p) change, since none of the exiting threads would
    be a group leader. That optimization only matters when the entire
    process exits.

    Does oprofile show any interesting differences?

    Paul


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