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SubjectRe: [PATCH] sched: wakeup buddy
On 03/11/2013 05:40 PM, Ingo Molnar wrote:
>
> * Michael Wang <wangyun@linux.vnet.ibm.com> wrote:
>
>> Hi, Ingo
>>
>> On 03/11/2013 04:21 PM, Ingo Molnar wrote:
>> [snip]
>>>
>>> I have actually written the prctl() approach before, for instrumentation
>>> purposes, and it does wonders to system analysis.
>>
>> The idea sounds great, we could get many new info to implement more
>> smart scheduler, that's amazing :)
>>
>>>
>>> Any objections?
>>
>> Just one concern, may be I have misunderstand you, but will it cause
>> trouble if the prctl() was indiscriminately used by some applications,
>> will we get fake data?
>
> It's their problem: overusing it will increase their CPU overhead. The two
> boundary worst-cases are that they either call it too frequently or too
> rarely:
>
> - too frequently: it approximates the current cpu-runtime work metric
>
> - too infrequently: we just ignore it and fall back to a runtime metric
> if it does not change.
>
> It's not like it can be used to get preferential treatment - we don't ever
> balance other tasks against these tasks based on work throughput, we try
> to maximize this workload's work throughput.
>
> What could happen is if an app is 'optimized' for a buggy scheduler by
> changing the work metric frequency. We offer no guarantee - apps will be
> best off (and users will be least annoyed) if apps honestly report their
> work metric.
>
> Instrumentation/stats/profiling will also double check the correctness of
> this data: if developers/users start relying on the work metric as a
> substitute benchmark number, then app writers will have an additional
> incentive to make them correct.

I see, I could not figure out how to wisely using the info currently,
but I have the feeling that it will make scheduler very different ;-)

May be we could implement the API and get those info ready firstly
(along with the new sched-pipe which provide work tick info), then think
about the way to use them in scheduler, is there any patches on the way?

Regards,
Michael Wang

>
> Thanks,
>
> Ingo
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