Re: [Qemu-devel] Basic block statistics

[Johan Rydberg]

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.

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.

-- 
Johan Rydberg, Free Software Developer, Sweden
http://rtmk.sf.net | http://www.nongnu.org/guss/