Messages in this thread | | | Date | Wed, 3 Aug 2016 13:31:30 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [RFC PATCH v7 1/7] Restartable sequences system call |
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On Wed, 3 Aug 2016, Andy Lutomirski wrote:
> > Well, a CMPXCHG without LOCK prefix isn't all that expensive on x86. > > > > It is however on PPC and possibly other architectures, so in name of > > simplicity supporting only the one variant makes sense. > > > > I wouldn't want to depend on CMPXCHG. But imagine we had primitives > that were narrower than the full abort-on-preemption primitive. > Specifically, suppose we had abort if (actual cpu != expected_cpu || > *aptr != aval). We could do things like: >
The latency issues that are addressed by restartable sequences require minimim instruction overhead. Lockless CMPXCHG is very important in that area and I would not simply remove it from consideration.
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