Matthew Helsley wrote:
On Sat, 2004-10-02 at 16:44, Hubertus Franke wrote: <snip>
along cpuset boundaries. If taskclasses are allowed to span disjoint cpumemsets, what is then the definition of setting shares ?
<snip>
I think the clearest interpretation is the share ratios are the same but the quantity of "real" resources and the sum of shares allocated is different depending on cpuset.
For example, suppose we have taskclass/A that spans cpusets Foo and Bar -- processes foo and bar are members of taskclass/A but in cpusets Foo and Bar respectively. Both get up to 50% share of cpu time in their respective cpusets because they are in taskclass/A. Further suppose that cpuset Foo has 1 CPU and cpuset Bar has 2 CPUs.
Yes, we ( Shailabh and I ) were talking about exactly that this afternoon. This would mean that the denominator of the cpu shares for a given class <cls> is not determined solely by the parents total_guarantee but by:
total_guarantee * size(cls->parent->cpuset) / size(cls->cpuset)
This is effectively what you describe below.
This means process foo could consume up to half a CPU while process bar could consume up to a whole CPU. In order to enforce cpuset partitioning, each class would then have to track its share usage on a per-cpuset basis. [Otherwise share allocation in one partition could prevent share allocation in another partition. Using the example above, suppose process foo is using 45% of CPU in cpuset Foo. If the total share consumption is calculated across cpusets process bar would only be able to consume up to 5% of CPU in cpuset Bar.]
This would require some changes in the CPU scheduler to teach the cpu-monitor to deal with the limited scope. It would also require some
mods to the API :
Since classes can span different cpu sets with different shares
how do we address the cpushare of a class in the particular context
of a cpu-set.
Alternatively, one could require that classes can not span different
cpu-sets, which would significantly reduce the complexity of this.
Cheers, -Matt Helsley
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