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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.

--
Regards/Gruss,
Boris.

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