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Date: Wed, 17 Aug 2011 11:03:26 -0700
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] qemu-thread: add TLS wrappers
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org

On 08/17/2011 10:51 AM, Blue Swirl wrote:
> >  Visual C++ supports __declspec(thread).
> >
> >  pthread TLS is orders of magnitudes slower than __thread.  __thread in an
> >  executable is just as fast as a non-TLS variable access, 2 or 3 machine
> >  language instructions at most.
> >
> >  Some pthread_getspecific implementation do a_linear walk_  of the keys.  In
> >  that case it may work to have something like Windows plus a single
> >  pthread_getspecific key.  On the other hand, Windows provides very good
> >  support for that thanks to its ordered subsections (.tls$something).  It
> >  only needs a bit of preprocessor magic.  Thinks such as linker scripts would
> >  be way out of scope.
>
> According to this blog, also pthread_getspecific on OSX can amount to
> three instructions except on PPC:
> http://lifecs.likai.org/2010/05/mac-os-x-thread-local-storage.html

I'll try to work out a DEFINE_TLS/DECLARE_TLS version for pthreads too.

BTW, __thread is in C1X too though I don't remember how they called it.

Paolo