Firefox 3 runs faster on Linux+Wine than on Linux -- comparative to running on Windows

[Reece Dunn]

2009/2/13 Susan Cragin <susancragin at earthlink.net>:
>>Hi,
>>
>>For those not monitoring slashdot [1], there is an article [2] that is
>>comparing the Google V8 benchmark on Windows and Linux versions of
>>Firefox 3.
>>
>>The result of this is that the Windows and Wine runs are pretty close
>>(241 vs 227) when compared to the Linux run (181) and Opera (155).
>>
>>I wonder what the results are like on Firefox 3.1 with tracemonkey
>>enabled on Windows, Wine and Linux.
>>
>>[1] http://tech.slashdot.org/article.pl?sid=09/02/13/0058251
>>[2] http://www.tuxradar.com/content/browser-benchmarks-2-even-wine-beats-linux-firefox
>>
>>- Reece
>
> One thing that interested me... one person wrote that Linux/Firefox compiled with msvc was faster than gcc, because msvc is better at optimization.
> Has anyone tried compiling wine with msvc?

Hi Susan,

WARNING: This is fairly technical, so apologies if this goes over your head!

The reason that Firefox javascript is faster when built with msvc
(according to the slashdot comments -- of which I am only part of the
way through) is because they use Profile Guided Optimization (PGO).

[sidebar]
This means that the code is compiled with special information that
records what methods and variables are being accessed. This program is
then run under normal usage patterns to gather profiling data. The
data collected here shows what the most common methods and variables
are.

The data is then fed into the linker along with the original program.
The linker can then use this information to organise the code so that
it performs better. That is, it uses the profile data to hint at where
to optimise the program (hence the name).
[/sidebar]

The commenters also point out that GCC (which is used to build Wine)
also has PGO capabilities. In order to do this, you need to record the
profile information for a given build. IIUC, you need to do this
manually for each build to gather the data for that build. NOTE: I am
not an expert on this, as I have only read bits and pieces on the
subject and not actually tried it out.

As for optimisation in general, I am not sure on how gcc compares with
msvc in terms of overall performance. Both allow you to optimise for
speed, size or balance the two. They both also allow you to do other
independent optimisations (e.g. target newer CPUs or enable enhanced
CPU instruction calls). Here, it is a matter of trying out different
combinations of options to get better results. NOTE: The distribution
versions of Firefox (and Wine) will be built to support older hardware
and thus won't benefit from taking advantage of the newer hardware
(Gentoo is your friend here :D).

For building Wine with msvc, I have had limited success building the
Wine components and (more specifically) tests with it, and have
contributed patches to help build more of them with msvc. In addition
to this, you will only be able to do this with a portion of the dlls
and components -- the ones that do not make use of any Linux
components.

Adding PGO support in Wine (which would have to be using gcc, since
the Wine program loader and other core components are likely to
benefit -- possibly the GDI and DirectX/WineD3D stuff as well).

It would be interesting to run a profiler on Wine with profile data
for different programs and games to see where the slow areas are.

The real benefit in terms of speed for Wine would be not to use msvc,
but to hand-optimise specific algorithms to take advantage of faster
assembly instructions. This would likely be for the cryptographic
algorithms (SHA1, MD5, etc), DirectX mathematic functions, GDI/DIB
code and pixel format transformations in DirectX/GDI. NOTE: These
should be done (if done at all) using the data from the profile runs
to see where the slow areas are.

I apologise for rambling, but hopefully this makes things clearer.

- Reece