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    SubjectRe: [patch 00/2] improve .text size on gcc 4.0 and newer compilers
    On Tue, Jan 03, 2006 at 09:51:17PM -0800, Martin J. Bligh wrote:
    > Matt Mackall wrote:
    >
    > >On Tue, Jan 03, 2006 at 03:40:59PM -0800, Martin J. Bligh wrote:
    > >
    > >
    > >>It seems odd to me that we're doing this by second-hand effect on
    > >>code size ... the objective of making the code smaller is to make it
    > >>run faster, right? So ... howcome there are no benchmark results
    > >>for this?
    > >>
    > >>
    > >
    > >Because it's extremely hard to design a benchmark that will show a
    > >significant change one way or the other for single kernel functions
    > >that doesn't also make said functions unusually cache-hot. And part of
    > >the presumed advantage of uninlining is that it leaves icache room for
    > >random other code that you're _not_ benchmarking.
    > >
    > >In other words, if it's not a microbenchmark, it generally can't be
    > >measured, directly or indirectly. And if it is a microbenchmark, the
    > >result is known to be biased.
    > >
    > >
    > Well, it's not just one function, is it? It'd seem that if you unlined
    > a whole bunch of stuff (according to this theory) then normal
    > macro-benchmarks would go faster? Otherwise it's all just rather
    > theoretical, is it not?

    Yes, if we uninline a big hunk of stuff, we should see results. But
    which hunk? Running benchmarks w/ and w/o Ingo's 3 patches should be
    educational. As would with -Os.

    Also note that there are going to be cases where smaller wins by
    orders of magnitude: where it makes the difference between the working
    set fitting in cache or RAM or not.

    > Cool, that sounds good. How much are we talking about?
    > I didn't see that in the thread anywhere ... perhaps I just
    > missed it, sorry it got long ;-)

    The out of line spinlock stuff went by about a year ago. Google for
    "zwane spinlock out of line".

    --
    Mathematics is the supreme nostalgia of our time.
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