Date:	Sun, 06 Apr 2008 00:29:20 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
CC:	Pavel Emelianov <xemul@...nvz.org>,
	Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [-mm] Add an owner to the mm_struct (v8)

Paul Menage wrote:
> On Sat, Apr 5, 2008 at 10:48 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>> Paul Menage wrote:
>>  > On Sat, Apr 5, 2008 at 7:47 AM, Balbir Singh <balbir@...ux.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, thats understandable

>>  >
>>  > 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?
> 

Yes, mostly. That's why I had made the virtual address space patches as a config
option on top of the memory controller :)

>>  >>  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.
> 

On the client side, each JVM instance exits after the test. I see the thread
group leader exit as well through getdelays (I see TGID exits).

> Does oprofile show any interesting differences?

Need to try oprofile.

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