Re: [Qemu-devel] [PATCH] target-sparc register window handling

[Aurelien Jarno <aurelien@aurel32.net>]

On Sat, Oct 06, 2012 at 12:15:16PM +0200, Aurelien Jarno wrote:
> On Fri, Oct 05, 2012 at 05:00:04PM -0700, Richard Henderson wrote:
> > This applies with or without the sparc-compare patch set I
> > recently sent, and it works with the same set of tests.
> > 
> > I've not had time to do true benchmarking on this, but it
> > does reduce the size of the generated code:
> 
> Experience proves that there is not a direct relation between size of
> the generated code and the resulting emulation speed, sometimes smaller
> code means slower emulation (when the code generation/optimization takes
> too much time), and sometimes bigger code might means faster emulation
> (think about replacing some helpers by TCG code).
> 
> As from the user point of view what is important is the emulation speed,
> I think benchmarks (even simple ones like measuring the boot time of a
> guest) are essential for this kind of patch.
> 

For what it worth, I measure a 4% slow down booting a sparc64 guest on a
Core-i5 2500 machine. I guess the memcpy() of the register windows is
more expensive that the gain on the TCG side, though it should be
probably be confirmed using some profiling tools.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net