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    SubjectRe: [rfc][patch] 1/2 Additional cpuset features


    > > But the jist of the matter is simple. Just as we (SGI) did with
    > > cpumemsets and perfmon on 2.4 kernels, so should we do with cpusets and
    > > perfmon on 2.6 kernels. And that is to perform this translation in
    > > perfmon code. Is it only SGI's dplace that requires the cpuset-relative
    > > numbering?
    > pfmon, sched_setaffinity, dplace. And this is only what I saw today.
    > Might develop into a longer list. The 2.4 solutions were rather
    > complicated.

    Are pfmon and dplace SGI specific? sched_affinity users already have to
    deal with potentially discontiguous cpu maps. Ive been teaching IBM
    applications about this fact as I find problems.

    > > The kernel-user boundary should stick to a single, system-wide, numbering
    > > of CPUs.
    > That leads to lots of complicated scripts doing logical -> physical
    > translation with the danger of access or attempting accesses to not
    > allowed CPUs. It may be easier to contain tasks into a range of cpus if
    > the CPUs in use are easily enumerable.

    I would think you could write this in your userspace library.

    > The patch would allow the use of the existing tools as if the machine
    > only had N cpus (as you said a soft partitioning of the machine). If
    > scripts are to be used with the current approach then they need to know
    > about all the CPUs in the system and perform the mapping. Its going to be
    > a nightmare to develop scripts that partition off a 512 cpu cluster
    > appropriately and that track the physical cpu numbers instead of the cpu
    > number within the cpuset.

    What happens when an application (or user) looks in /proc/cpuinfo?
    And how does /sys/.../cpus match? Also what happens when you hotplug out
    a cpu and your memory map becomes discontiguous?

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