Whopping 5% for GCC...
Posted Oct 18, 2008 18:18 UTC (Sat) by khim
In reply to: x86_64 is also faster ? Not so fast...
Parent article: Linux now an equal Flash player (Linux-Watch)
Perhaps but the average win on typical GNU/Linux systems is
greater than that: GCC does not do so well on register starved platforms.
Find a comparison on GCC and you the difference is greater because x86 is
really quite register starved.
GCC was really, really bad on register starved architectures, but since
IA32 was the most important architectures for many years it got many tricks
which helped. This difference is not so
great with gcc too: 5.2%.
Additionally, x86_64 makes mandatory a number of micro-
architectural improvements which were previously optional. For example,
consider SSE2 which is not universally available on x86.
Very few systems today don't have SSE2. Athlon XP was discontinued three
years ago and even VIA
C7 and Intel Atom
support SSE2 today - but they don't support x86-64!
So generally distributed binaries must either offer alternative
functions and detect at run time, or, more commonly, avoid using those
1. There are yet another alternative: barf and refuse to run. Few
systems will be affected.
2. Flash was written long ago - so MMX/SSE/SSE2 versions of all routines
And I'm not sure why you say that ~3% by itself isn't all that
compelling when the price difference between a 2.83GHz core2 quad and a
3.0GHz core 2 quad cpu is $230 US. Based on that simplistic analysis we
might expect 3% to be worth $115 US while if you use a modern x86_64-
painless distro and don't use non-free software the cost of 64bit mode is
pretty close $0.
Because average difference of just 3% with difference from -40% to 30%
in case by case basis means even bigger win will be to carefully select
which programs must be 32bit and which - 64bit. And win from profile based
optimization and whole program optimizations can dwarf that 3-5% in many
cases - but nobody does that. It looks kinda hypocritical to press Adobe to
rewrite the Flash for mere 3-5% win when Linux community does not do it's
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