On Sat, 17 Dec 2005, Linus Torvalds wrote:
> Of the other architectures you list, only ARM is really important. And no,
> arm doesn't do swap. It does LL/SC (except they call it "ldrex/strex",
> which I assume stands for "load/store with reservation and X just because
> X is cool. Yeah, we're cool" (*)).
Well, if you really want to be honest, you have to consider that the
ldrex/strex instructions are available only on ARM architecture level 6
and above, or in other words with only about 1% of all ARM deployments
out there. The other 99% of actual ARM processors in the field only
have the atomic swap (swp) instruction which is insufficient for
implementing a counting semaphore (we therefore have to disable
interrupts, do the semaphore update and enable interrupts again which is
much slower than a swp-based mutex).
Nicolas
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