Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

[Michael Wang <wangyun@linux.vnet.ibm.com>]

On 02/22/2013 04:36 PM, Peter Zijlstra wrote:
> On Fri, 2013-02-22 at 10:37 +0800, Michael Wang wrote:
>> But that's really some benefit hardly to be estimate, especially when
>> the workload is heavy, the cost of wake_affine() is very high to
>> calculated se one by one, is that worth for some benefit we could not
>> promise?
> 
> Look at something like pipe-test.. wake_affine() used to ensure both
> client/server ran on the same cpu, but then I think we added
> select_idle_sibling() and wrecked it again :/
> 
> $ taskset 1 perf bench sched pipe
> # Running sched/pipe benchmark...
> # Extecuted 1000000 pipe operations between two tasks
> 
>      Total time: 3.761 [sec]
> 
>        3.761725 usecs/op
>          265835 ops/sec
> 
> $ perf bench sched pipe
> # Running sched/pipe benchmark...
> # Extecuted 1000000 pipe operations between two tasks
> 
>      Total time: 29.809 [sec]
> 
>       29.809720 usecs/op
>           33546 ops/sec
> 

Ok, it do looks like wake_affine() lost it's value...

> 
> Now as far as I can see there's two options, either we find there's
> absolutely no benefit in wake_affine() as it stands today and we simply
> disable/remove it, or we go fix it. What we don't do is completely
> wreck it at atrocious cost.

I get your point, we should replace wake_affine() with some feature
which could really achieve the goal to make client and server on same cpu.

But is the logical that the waker/wakee are server/client(or reversed)
still works now? that sounds a little arbitrary to me...

Regards,
Michael Wang

> 
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