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Re: Remove sparcv8 support
On Thu, 2016-11-10 at 13:22 -0500, Chris Metcalf wrote:
> On 11/10/2016 12:08 PM, Torvald Riegel wrote:
> > Looking at tile's atomic-machine.h files again, it seems we're not
> > actually enforcing that atomic stores are atomic wrt. the CAS
> > implementation in the kernel.
> > The default implementation for atomic_store_relaxed in include/atomic.h
> > does a plain memory store instead of falling back to exchange. This is
> > the right approach by default, I think, because that's what
> > pre-C11-concurrency code in glibc does (ie, there's no abstraction for
> > an atomic store at all, and plain memory accesses are used).
> > However, if we emulate CAS with locks or such in the kernel, atomic
> > stores need to synchronize with the CAS. This would mean that all archs
> > such as tile or sparc that do that have to define atomic_store_relaxed
> > to fix this (at least for code converted to using C11 atomics, all
> > nonconverted code might still do the wrong thing).
> Note that our mainstream tilegx architecture has full atomic support, so
> this is only applicable to the older tilepro architecture.