Re: [patch 00/21] mutex subsystem, -V14


* Joel Schopp <jschopp@xxxxxxxxxxxxxx> wrote:

> > Shouldn't you make that "isync" dependent on SMP too? UP doesn't
> > need it, since DMA will never matter, and interrupts are precise.
>
> I think the isync is necessary to keep heavily out of order processors
> from getting ahead of themselves even on UP. Scanning back through
> the powerpc spinlock code they seem to take the same view there as
> well.

the asm/spinlock.h ops are only built on SMP kernels. mutex.h is for
both UP and SMP. On UP you should need no synchronization, because the
only way another context could interfere with your critical section is
by getting interrupted, and interrupts are fully synchronizing, right?
On UP the only synchronization needed is when a device reads/writes
memory in parallel to the CPU.

Ingo
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