vmstat's entries type

[Peter Jeremy]

On Sun, 2006-Jul-30 11:07:31 +0200, Michal Mertl wrote:
>Paul Allen wrote:
>> Which FreeBSD tier-I 64b arch do you have in mind...
>
>I was referring to what Peter Jeremy said earlier in this thread:
>
>> RISC architectures usually only have TAS lock primitives (because "inc
>> mem" doesn't exist) and so require a spinlock to perform an atomic
>> update.

This was based on an examination of /usr/src/sys/*/include/atomic.h.
It looks like I was overly quick because the RISC architectures are
using compare-and-swap, rather than test-and-set primitives - sorry
about the error.  The details are:
- Alpha (RIP) used a loop around a locked conditional store
- amd64 appears to support RMW
- arm doesn't support 64-bit atomic operations
- i386 doesn't support 64-bit atomic operations (but could implement them
  using cmpxchg8b in a loop)
- ia64 uses cmpxchg in a loop
- ppc doesn't support 64-bit atomic operations
- sparc64 uses cas in a loop.

Whilst true spinlocks are not needed, amd64 is the only architecture
FreeBSD supports that does not require some sort of loop to perform
a 64-bit atomic operation.

-- 
Peter Jeremy
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