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

    In the rare case of functions that are extremely popular (like
    spinlock and friends), we _can_ actually see small improvements in
    macrobenchmarks like kernel compiles. So it's fairly reasonable to
    assume that reducing icache footprint really does matter more than
    cycle count and extrapolate that to other functions.

    (Unfortunately, Zwane is an enemy of history and the URL for the
    benchmarks he posted for out-of-line spinlock has gone stale.)

    --
    Mathematics is the supreme nostalgia of our time.
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