Re: [Qemu-devel] [PATCH 05/30] exec: do not use qemu/tls.h

[Peter Maydell]

On 1 July 2013 11:45, Paolo Bonzini <address@hidden> wrote:
> Il 29/06/2013 12:55, Peter Maydell ha scritto:
>> We should just be consistent and always make this be
>> per-thread.
>
> If it's okay to make cpu_single_env accesses more expensive by a factor
> of 4 on TLS-deficient hosts (at least OpenBSD; do Darwin and NetBSD
> support thread-local storage?), I'm all for it.  I (and I guess Stefan
> too) do not want to introduce performance regressions in these patches.
>  Making it simpler is something that one would do after having tested at
> least one of OpenBSD/Darwin/whatever.

MacOSX 10.8 supports __thread if you build with clang (not if you
build with gcc), though I can't speak to its performance since it
compiles to a function call to get the variable's address.

> This patch does not make things worse than before.  If anything, it's
> better because *more* targets have non-TLS semantics: namely non-KVM
> targets on Linux become non-TLS.

That is making things worse! Non-TLS is the untested minority
case, we want to be taking things out of it, not pushing
configs that were previously TLS into it.

-- PMM