Re: Why Semaphore Hardware-Dependent?

[David Howells]

Christoph Lameter <clameter@xxxxxxx> 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
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