Re: [Qemu-devel] Basic block statistics

[Fabrice Bellard]

Johan Rydberg wrote:
> Johan Rydberg <address@hidden> wrote: (Yes, I did)
>
> : I have yet not figured out a way to alter QEMU to see how much of
> : the execution time these blocks consume.  Say that the ~2.38% of
> : the blocks consume 10% of the time, it might be worth doing extra
> : optmizations on then.  Fabrice, do you know how I could hack QEMU
> : to get this kind of information?
>
> I disabled chaining and counted each invoking of basic blocks, and
> maintained a separate counter for those blocks that contain internal
> loops.  Booting the Debian image to the login prompt gave that the
> blocks with internal loops stod for 33.7% of all invoked blocks.
> Can anyone verify this? (by hacking QEMU yourself, both verifying
> the numbers and that I collect the statistics correctly)  It should
> not take more than 20 minutes all together.

I would have done about the same to get the stats :-) I read that wabi 
was able to optimize these kind of loops, so I guess it is really 
interesting.

> Assume that the values are correct.  Then optimization of the blocks
> that contain loops could result in a rather huge performance boost.
> You could for example try to move register stores and loads out of
> the it and just work with host registers in the actual loop.

I don't have time yet to optimize QEMU, but I'll think about that. Of 
course if someone does the patch I will accept it !

Fabrice.