Messages in this thread |  | | | Date | Tue, 6 Dec 2005 21:06:07 +0100 | | From | Andi Kleen <> | | Subject | Re: [RFC 1/3] Framework for accurate node based statistics |
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On Tue, Dec 06, 2005 at 11:36:43AM -0800, Christoph Lameter wrote: > On Tue, 6 Dec 2005, Andi Kleen wrote: > > > > Yuck. That code uses atomic operations and is not aware of atomic64_t. > > Hmm? What code are you looking at? > include/asm-generic/local.h. this is the default right? And > include/asm-ia64/local.h. > > > At least i386/x86-64/generic don't use any atomic operations, just > > normal non atomic on bus but atomic for interrupts local rmw. > > inc/dec are atomic by default on x86_64?
They are atomic against interrupts on the same CPU. And on Linux also atomic against preempt moving you to another CPU. And all that without the cost of a bus lock. And that is what local_t is about.
> > > Do you actually need 64bit? > > 32 bit limits us in the worst case to 8 Terabytes of RAM (assuming a very > small page size of 4k and 31 bit available for an atomic variable > [sparc]). SGI already has installations with 15 Terabytes of RAM.
Ok we'll need a local64_t then. No big deal - can be easily added. Or perhaps better a long_local_t so that 32bit doesn't need to pay the cost.
-Andi
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