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SubjectRe: [-mm] Add an owner to the mm_struct (v8)
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?

>> If the user is unable to remove a cgroup node, it will
>> be due a valid reason, the group_leader is still around, since the threads are
>> still around. The user in that case should wait for notify_on_release.
>>
>> >
>> > To me, it seems that setting up a *virtual address space* cgroup
>> > hierarchy and then putting half your threads in one group and half in
>> > the another is asking for trouble. We need to not break in that
>> > situation, but I'm not sure it's a case to optimize for.
>>
>> That could potentially happen, if the virtual address space cgroup and cpu
>> control cgroup were bound together in the same hierarchy by the sysadmin.
>
> 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.

>> 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.

> How many runs was that over? Ingo's recently posted volanomark tests
> against -rc7 showed ~3% random variation between runs.

I ran the test four times. I took the average of runs, I did see some variation
between runs, I did not calculate the standard deviation.

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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