Andi Kleen <[email protected]> wrote:
>
> On Thursday 09 February 2006 19:04, Andrew Morton wrote:
> > Ashok Raj <[email protected]> wrote:
> > >
> > > The problem was with ACPI just simply looking at the namespace doesnt
> > > exactly give us an idea of how many processors are possible in this platform.
> >
> > We need to fix this asap - the performance penalty for HOTPLUG_CPU=y,
> > NR_CPUS=lots will be appreciable.
>
> What is this performance penalty exactly?
All those for_each_cpu() loops will hit NR_CPUS cachelines instead of
hweight(cpu_possible_map) cachelines.
> It wastes quite some memory (each possible CPU needs 32K of memory which
> adds quickly up), but it shouldn't impact other CPU use.
>
> >
> > Do any x86 platforms actually support CPU hotplug?
>
> Xen does.
yup.
> And it's needed for suspend/resume on normal x86 now.
True.
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