On Jun 24, 2010, at 11:50 AM, Taras Glek <tg...@mozilla.com> wrote:
Hi,
Just wanted to give a heads up on what might be the biggest compiler-
upgrade-related performance difference we've seen at Mozilla.
We switched gcc4.3 for gcc4.5 and our automated benchmarking
infrastructure reported 4-19% slowdown on most of our performance
metrics on 32 and 64bit Linux.
A lone 8% speedup was measured on the Sunspider javascript benchmark
on 64bit linux.
Here are some of the slowdowns reported:
http://groups.google.com/group/mozilla.dev.tree-management/browse_thread/thread/77951ccb76b5e630#
http://groups.google.com/group/mozilla.dev.tree-management/browse_thread/thread/624246d7d900ed41#
Most of the code is compiled with -fPIC -fno-rtti -fno-exceptions
-Os
Stop right there. You are compiling at -Os, that is tuned for size and
not speed. So the question is did the size go down? Not the speed
decreased. Try at -O2 and report back. I doubt we are going to do a
tradeoff for speed at -Os at all.
Thanks,
Andrew Pinski
-freorder-blocks -fomit-frame-pointer. The only difference in 4.5 is
that we link with -static-libstdc++ and compile libstdc++ with -
fPIC. However we barely make use of libstdc++, so I doubt that's the
problem. We needed to link statically because of 4.5 uses a handful
of newer libstdc++ symbols.
We were upgrading to gcc 4.5.0 because of plugins and the fact that
it can compile Firefox with PGO on(above builds were not built with
PGO). Now we have to reconsider a complete switchover to 4.5.
I'm not sure how to proceed from here,
Taras
