cachepolicy on arm UP/SMP

Catalin Marinas catalin.marinas at
Wed Apr 27 13:10:34 EDT 2011

2011/4/2 rocky <bill_carson at>:
> I am a little confused about arm cachepolicy for UP/SMP.
> in arch/arm/mm/mmu.c
> for UP , default cache policy is CPOLICY_WRITEBACK;
> while for SMP, cache policy is overrided with  WRITEALLOC.
> why does SMP cannot use WRITEBACK?
> It is about coherency issue?

Historical reasons I think because ARM11MPCore only supported WBWA
caches, though even if only WB configuration was set.

Note that WB or WBWA is just a hint and the processor is allowed to do
write allocation or ignore it. We could simply make both the same at
least on ARMv6+ hardware (and I'm more in favour of WBWA).


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