Peter Williams wrote:
>>>>
>>>>The problem is that with per-task caps, if I have a resource group A
>>>>and I want to limit it to 10%, I need to limit each task in resource
>>>>group A to 10% (which makes resource groups not so useful). Is my
>>>>understanding correct?
>>>
>>>
>>>Well the general idea is correct but your maths is wrong. You'd have
>>>to give each of them a cap somewhere between 10% and 10% divided by
>>>the number of tasks in group A. Exactly where in that range would
>>>vary depending on the CPU demand of each task and would need to be
>>>adjusted dynamically (unless they were very boring tasks whose demands
>>>were constant over time).
>>>
>>
>>
>>Hmm.. I thought my math was reasonable (but there is always so much to
>>learn)
>> From your formula, if I have 1 task in group A, I need to provide it with
>>a cap of b/w 10 to 11%. For two tasks, I need to give them b/w 10 to 10.5%.
>>If I have a hundred, it needs to be b/w 10% and 10.01%
>
>
> Now your arithmetic is failing you. According to my formula:
>
> 1. With one task in group A you give it 10% which is what you get when
> you divide 10% by one.
>
> 2. With two tasks in group A you give them each somewhere between 5%
> (which is 10% divided by 2) and 10%. If they are equally busy you give
> them each 5% and if they are not equally busy you give them you give
> them larger caps.
Yes, I understand. I misinterpreted what you said earlier. I see you
clearly meant the range [cap_of_the_group/number_of_tasks, cap_of_the_group]
>
> Another, probably a better but more expensive, formula is to divide the
> 10% between them in proportion to their demand. Being careful not to
> give any of them a zero cap, of course. I.e. in the two task 10% case
> they each get 5% if they are equally busy but if one is twice as busy as
> the other it gets a 6.6% cap and the other gets 3.3% (approximately).
>
Yes, that makes a lot of sense
> Peter
Thanks for clarifying.
--
Balbir Singh,
Linux Technology Center,
IBM Software Labs
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