Re: Why Semaphore Hardware-Dependent?

[Christoph Lameter]

On Tue, 29 Aug 2006, David Howells wrote:

> Ralf Baechle <ralf@xxxxxxxxxxxxxx> wrote:
> 
> > > Which arches do not support cmpxchg?
> > 
> > MIPS, Alpha - probably any pure RISC load/store architecture.
> 
> 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.

> 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.

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