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

[Matt Mackall <mpm@selenic.com>]

On Thu, Jan 05, 2006 at 01:19:12PM +0100, Arjan van de Ven wrote:
> 
> > What would be nice to do is pack all the frequently used code together 
> > in close proximity. Would probably have much larger effects with 
> > userspace code, esp where we touch disk (which is more page-size 
> > granularity), but is probably worth doing with kernel code too (where 
> > AFAICS we'd only get cacheline granular).
> 
> in the kernel we could make a .text.rare section for functions, which we
> could annotate with __rare.
> The other way around, __fastpath or whatever is a bad idea, everyone
> will consider all of their own functions as such (just like inline ;)...
> go-fast-stripes all the way :-(

Gah, we don't want to do this by hand in either direction. It's the
inline nightmare all over again.

It'd be better to take a tool like oprofile and run it against some
test suite to generate a usage map, then re-sort based on the map.
Then ship a "standard" map in the stock tarball. Note that the map
need only list the popular functions.

The ideal sampling tool can collect second order information: which
functions are executed near each other as well as which are executed
most frequently.

-- 
Mathematics is the supreme nostalgia of our time.