Re: Why Semaphore Hardware-Dependent?

David Howells
2006-08-29T16:57:50Z

Christoph Lameter <clameter@sgi.com> wrote:

> > Some of these have LL/SC or equivalent instead, but ARM5 and before, FRV,
> > M68K before 68020 to name but a few.
>
> This is all pretty ancient hardware, right? And they are mostly single
> processor so no need to worry about concurrency. Just disable interrupts.

No, they're not all ancient h/w, and "just disabling interrupts" can be really
expensive.

> > And anything that implements CMPXCHG with spinlocks is a really bad
> > candidate for CMPXCHG-based rwsems.
>
> Those will optimize out if it is a single processor configuration.

Not necessarily. Consider preemption.

David