On Wed, 2012-06-13 at 16:54 +0200, Vincent Guittot wrote:

On 13 June 2012 15:07, Peter Zijlstra [off-list ref] wrote:

quoted

On Tue, 2012-06-12 at 14:02 +0200, Vincent Guittot wrote:

quoted

+struct cpu_capacity cpu_capacity[NR_CPUS];

I know ARM isn't likely to suffer from the 4k cpu issue, but is there a
reason to use a NR_CPUS array over a per-cpu variable?

At this stage, we don't know which logical CPU will match which hwid.
During the boot of each CPU, we parse the table to found an efficiency
value for the booting CPU. The whole table is used by one CPU at a
time.

Its not so much the usage as the dynamic sizing that I was after.
NR_CPUS will always be the max size, whereas per-cpu data will only use
the amount of storage required to back the number of cpus present.

For this reason we've spend a great deal of effort to remove NR_CPUS
sized arrays all over the core (and x86/ia64 arch) code, since distros
now build with NR_CPUS=4096 but hardly anybody has that many cpus, so
arrays sized that way waste tons of resources.