Re: [patch 00/2] improve .text size on gcc 4.0 and newer compilers

Matt Mackall
2006-01-05T23:10:10Z

On Thu, Jan 05, 2006 at 02:49:21PM -0800, Martin Bligh wrote:
>
> >>>What I was proposing was something like, say, arch/i386/popularity.lst,
> >>>which would simply contain a list of the most popular n% of functions
> >>>sorted by popularity. As text, of course.
> >>
> >>I suspect that would certainlty work for pure function-based popularity,
> >>and yes, it has the advantage of being simple (especially for something
> >>that ends up being almost totally separated from the compiler: if we're
> >>using this purely to modify link scripts etc with special tools).
> >>
> >>But what about the unlikely/likely conditional hints that we currently do
> >>by hand? How are you going to sanely maintain a list of those without
> >>doing that in source code?
> >
> >
> >Dunno. Those bits are all anonymous so marking them in situ is about
> >the only way to go. But we can do better for whole functions.
>
> Would also make it easier to rank it as a percentage, or group by
> locality of reference to other functions, rather than just a binary
> split of "rare" vs "not-rare".
>
> Of course it's all very dependant on workload, which drivers you're
> using too, etc, etc. So a profile that's separate also makes it much
> easier to tweak for one machine than the source base in general, which
> theoretically represents everyone (and thus has little info ;-)).
>
> Which also makes me think it's easier to mark hot functions than cold
> ones, in a more general maintainance sense.

Yes, I think it definitely makes sense to think in terms of hot
functions. We surely have a nice long tail on the popularity
distribution and only the first 5% or so are actually worth sorting
and packing.

--
Mathematics is the supreme nostalgia of our time.