Re: [Qemu-devel] env in TLS

[Fabrice Bellard <fabrice@bellard.org>]

Using TLS seems a good idea. I hesitated to implement it because I was 
not sure that segment overrides were as fast as an indexed memory access 
on all x86 processors. I think that imposing a gcc version >= 3.2 is no 
longer an issue. We must be sure that the other platforms support the 
__thread keyword though.

Fabrice.

Piotr Krysik wrote:
> Hi!
> 
> Fabrice, how about moving env variable to TLS?
> 
> This could improve performance (based on 
> http://lists.gnu.org/archive/html/qemu-devel/2004-09/msg00294.html
> 
> about 10% could be gained -- need to verify). Also 
> additional register would be available for op.c 
> (anyone to implement register renaming?).
> 
> The main problem with this approach is portability. 
> AFAIK GCC <= 3.2 doesn't recognize __thread keyword. 
> For x86 we could fall-back to the LDT method from 
> qemu-fast. How about other platforms? In the worst 
> case we could use global variable and forget about 
> multi-processor qemu-softmmu and multi-thread in 
> qemu-user for some platforms in the future.
> 
> 
> Comments?
> 
> Piotrek
> 
> 
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