Re: function ordering (was: Re: [RFC] exit_thread() speedups in x86 process.c)

[Arjan van de Ven <arjan@infradead.org>]

On Sun, 2005-07-03 at 13:30 +0100, Hugh Dickins wrote:
> On Sun, 3 Jul 2005, Arjan van de Ven wrote:
> > 
> > hmm. I wonder if a slightly different approach (based on the __slow)
> > idea would make sense
> > 1) Use -ffunction-sections option from gcc to put each function in it's
> > own section
> > 2) Use readprofile/oprofile data to collect an (external to the code)
> > list of hot/cold functions (we can put a default list in the kernel
> > source somewhere and allow people to measure their own if they want)
> > 3) Use this list to make a linker script to order the functions
> > 
> > this way we don't need to put a lot of __slow's in the code *and* it's
> > based on measurements not assumptions, and can be tuned for a specific
> > situation in addition.
> 
> This is reminiscent of "fur", whose source Old SCO opened.
> Google for SCO fur: amidst all the hits about "fur flying"
> you might find something useful!

it's also similar to the idea to Nat's grope ;)
it's just a lot easier for the kernel than for the average userspace
since we already have linker scripts

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