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SubjectRe: [patch v4 05/18] sched: quicker balancing on fork/exec/wake
On 02/12/2013 06:22 PM, Peter Zijlstra wrote:
> On Thu, 2013-01-24 at 11:06 +0800, Alex Shi wrote:
>> Guess the search cpu from bottom to up in domain tree come from
>> commit 3dbd5342074a1e sched: multilevel sbe sbf, the purpose is
>> balancing over tasks on all level domains.
>> This balancing cost too much if there has many domain/groups in a
>> large system.
>> If we remove this code, we will get quick fork/exec/wake with a
>> similar
>> balancing result amony whole system.
>> This patch increases 10+% performance of hackbench on my 4 sockets
>> SNB machines and about 3% increasing on 2 sockets servers.
> Numbers be groovy.. still I'd like a little more on the behavioural
> change. Expand on what exactly is lost by this change so that if we
> later find a regression we have a better idea of what and how.
> For instance, note how find_idlest_group() isn't symmetric wrt
> local_group. So by not doing the domain iteration we change things.
> Now, it might well be that all this is somewhat overkill as it is, but
> should we then not replace all of it with a simple min search over all
> eligible cpus; that would be a real clean up.

Um, will think this again..


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