On Thu, Feb 23, 2012 at 2:55 PM, Nikos Chantziaras <rea...@arcor.de> wrote: > On 23/02/12 21:42, Michael Mol wrote: >> >> On Thu, Feb 23, 2012 at 2:36 PM, Nikos Chantziaras<rea...@arcor.de> >> wrote: >>> >>> On 23/02/12 12:44, Mick wrote: >>>> >>>> The irony is that older boxen which would benefit most from building >>>> from >>>> source are constrained in resources to achieve this and have to resort >>>> to >>>> installing bin packages. >>> >>> >>> I doubt that the bin package will be slower than the one compiled from >>> source. I predict the reverse, in fact. The bin package will perform >>> better. >> >> >> That seems a strange prediction. What drives that hunch? > > > The PGO optimized build that Mozilla is shipping. You can also build with > PGO from source, but that means building FF *twice* in a row (by enabling > the "pgo" USE flag). I doubt that with the old laptop anyone is building FF > twice with PGO, and that means that the -bin package should be faster. > > Furthermore, FF is build using its own CFLAGS. They are the same in the > source build as well as in the -bin package. The only difference is > probably the -march option. And that doesn't make much difference to begin > with (after -march=i686, gains are very minimal).
I knew and forgot about PGO, but I didn't realize there was a USE flag for it. Neat. I'll be enabling that. I disagree with the idea that keeping things down around -march=i686 provides only minimal gains. SSE and SSE2 instructions carry a big benefit for numerical operations, especially those which can be parallelized, but not enough to justify batching into a GPU. AVX will be adding operations which allow more useful and flexible use of registers. Simply bumping up to x86-64 from simple x86 doubles your GPRs, which gives the compiler all kinds of room to work with. If the combination of those things doesn't significantly benefit a program written in C or C++, then I suspect there's something dreadfully wrong with the architecture of that codebase. -- :wq
