On Tue, Feb 21, 2006 at 07:24:15AM -0800, Chandra Seetharaman wrote:
> I think Vatsa is differentiating between "hard limit"(class will not get
> any resource and the surplus resources will be wasted) and "soft
> limit" (class can get resource over its soft limit if there is surplus).
Yes, this is what I meant earlier.
> IMO, advantage of using "soft limit" is that it can be used as a
> relative priority when surplus resources are to be allocated to classes.
>
> For example, consider 3 classes, which are CPU hogs, with soft limits
> Class A 20%
> Class B 25%
> Class C 30%
> and when all of them reached their soft limit(total usage 75%), the
> remaining 25% can be divided between them proportional to their soft
> limit. i.e
> Class A would get => 25 * 20/(20+25+30) ==> 6.66%
> Class B would get => 25 * 25/(20+25+30) ==> 8.33%
> Class C would get => 25 * 30/(20+25+30) ==> 10%
The above calculation may not be that straightforward if not everyone is
CPU hog. Consider this case:
Class A 20% -> CPU Hog
Class B 25% -> Not a CPU Hog
Class C 30% -> Not a CPU Hog
Class D 25% -> CPU Hog
The remaining in this case is 0%, yet we may have surplus cycles (because of
underutilization by B and C). In this case "surplus" CPU cycles that has to be
distributed b/n A & D has to be calculated dynamically. Not sure how much of
overhead it imposes (SMP may make it more complex because of load balance
issues?).
--
Regards,
vatsa
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