Re: [PATCH] percpu data: only iterate over possible CPUs

Heiko Carstens a écrit :
tree 8c30052a0d7fadec37c785a42a71b28d0a9c5fcf
parent cef5076987dd545ac74f4efcf1c962be8eac34b0
author Eric Dumazet <dada1@xxxxxxxxxxxxx> Sun, 05 Feb 2006 15:27:36 -0800
committer Linus Torvalds <torvalds@xxxxxxxxxxx> Mon, 06 Feb 2006 03:06:51 -0800

[PATCH] percpu data: only iterate over possible CPUs

percpu_data blindly allocates bootmem memory to store NR_CPUS instances of
cpudata, instead of allocating memory only for possible cpus.

As a preparation for changing that, we need to convert various 0 -> NR_CPUS
loops to use for_each_cpu().

(The above only applies to users of asm-generic/percpu.h. powerpc has gone it
alone and is presently only allocating memory for present CPUs, so it's
currently corrupting memory).

This patch is broken since it replaces several loops that iterate NR_CPUS
times with for_each_cpu before cpu_possible_map is setup:

This patch assumes that cpu_possible_map is setup before setup_per_cpu_areas().

That sounds a reasonable assumption, but maybe not on your architecture ?

I dont think cpu_possible_map has to be filled at smp_prepare_cpus() time, but long before.

On i386/x86_64/ia64, this is done from setup_arch() called from start_kernel() just before setup_per_cpu_areas()

On powerpc it's done from setup_system(), called before start_kernel()

Eric


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