Messages in this thread | | | Date | Fri, 10 Feb 2006 02:42:22 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] percpu data: only iterate over possible CPUs |
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Andi Kleen <ak@muc.de> wrote: > > On Thursday 09 February 2006 19:04, Andrew Morton wrote: > > Ashok Raj <ashok.raj@intel.com> 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.
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