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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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