Re: [Qemu-devel] Profiling Qemu for speed?

[Daniel Egger]

On 18.04.2005, at 11:51, Ian Rogers wrote:

> I'm not sure if you can get GCC to generate code sequences like this, 
> but you probably at least need to use the -fprofile-generate and 
> -fprofile-use options
> http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

Feedback optimisation (FDO) will not work for two reasons:
a) qemu itself is something like a realtime compiler so FDO
   will only speed up the compiler but not the generated code
b) FDO will only provide speed boosts if the feedback phase
   has a chance to analyse a representative work pattern that
   is hopefully also repetitive

After all FDO is mostly about making a tradeoff size/speed
and rearranging code (mostly branches) to avoid branch
mispredictions of the CPU.

Servus,
      Daniel

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