Re: cacheline alignment and per-cpu data

[Jes Sorensen <jes@sgi.com>]

>>>>> "Chase" == Chase Venters <chase.venters@clientec.com> writes:

Chase> On Fri, 9 Jun 2006, Chris Friesen wrote:
>> Will this cause cacheline pingpong?  If I do this sort of thing do
>> I need to ensure that the struct is a multiple of cacheline size
>> (or specify cacheline alignement)?

Chase> Yes. If CPU 2 tries to write to struct member 1 of array
Chase> element 2, and array element 1 is in CPU 1's cache, it must be
Chase> invalidated.

Chase> GCC (and kernel macros) provide good support for enforced
Chase> cacheline alignment, but it's also possible to pad your
Chase> structures.

Best way to go is to use __cacheline_aligned rather than try to get
the padding right manually. Someone will add a field somewhere in the
middle and mess it up and nobody notices.

Cheers,
Jes