Messages in this thread |  | | | Date | Thu, 30 Apr 2009 12:11:26 -0400 (EDT) | | From | Christoph Lameter <> | | Subject | Re: [PATCH] Fix dirty page accounting in redirty_page_for_writepage() |
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On Thu, 30 Apr 2009, Ingo Molnar wrote:
> > may not care too much about a event counter missing a beat once in > > a while for platforms not supporting atomic per cpu ops. I know > > this affects IA64. The cost of an atomic operations for an event > > counter update (which would have avoided the potential of a > > concurrent update) was not justifiable. > > when you say "atomics", do you mean the classic meaning of atomics? > Because there are no classic atomics involved. This is the > before/after disassembly from Eric's commit 4e69489a0:
The fallback for IA64 would be to use full (classic) atomic operations (fetchadd) instead of fast atomic vs. interrupt as available on x86
> c0436275: 64 83 05 20 5f 6a c0 addl $0x1,%fs:0xc06a5f20 > > There's no atomic instructions at all - the counters here are only > accessed locally. They are local-irq-atomic, but not > cacheline-atomic.
Right but that is not available on IA64. So one must choose between manually disabling interrupts and then increment the counter (long code sequence) and a classic atomic operation for the fallback.
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