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    SubjectRe: [PATCH] x86, msr: add support for non-contiguous cpumasks
    On Thu, Dec 10, 2009 at 05:49:02PM -0800, H. Peter Anvin wrote:
    > On 12/07/2009 04:21 AM, Borislav Petkov wrote:
    > >
    > > struct msr {
    > > + int cpu;
    > > union {
    > > struct {
    > > u32 l;
    > I really don't like this patch, for multiple reasons. One of them is
    > the above: this has no business being part of struct msr, which reflects
    > an MSR value (and ideally should replace at least the use of two
    > pointers in other places over time). Having a CPU field and not an MSR
    > number field particular doesn't make any sense.

    Why, MSRs are per-CPU. My reasoning here is to reflect the value of an
    MSR on a particular CPU...


    > The ideal probably would be to use a percpu variable. Now, this would
    > either have to be a dynamic percpu allocation (which would have to be
    > the responsibility of the caller, and reused, lest this would be a
    > *very* expensive proposition), or we would have to make these functions
    > run under a mutex. However, as long as the expected callers of this are
    > things that get set up once and then pretty much stick around, a percpu
    > variable might just work.

    I think this would be the cleanest way. Also, best it'll be to allocate
    those dynamically only when they're really needed (e.g. on driver
    loading) and later reuse them.


    > The third option would be to at least require that the struct msr
    > contents are at least serial in the order of the bitmask, not by adding
    > another field.

    I had that version already done but it seemed half-baked and clumsy for
    the MSRs array to traverse. I'll give the percpu variables a shot and
    get back to you when I have something ready.

    Thanks for reviewing.


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