On Sun, 28 Dec 2003, Arnaldo Carvalho de Melo wrote:
>
> Please apply on top of your 2.6.0-tiny1 tree, CC to netdev for
> eventual comments.
Please don't do it this way.
This is quite possibly faster even _normally_, so it might make more sense
to just do it globally instead of having a CONFIG_NEX_SMALL.
Basically, inline functions tend to win only when inlining them is smaller
and simpler than actually calling a function. The most common cause of
that is that some argument is commonly constant (and thus gets simplified
away by inlining), or the function itself literally expands to just a few
instructions (the list functions, the inline asms for things like "cli"
etc).
We use a lot too many inline functions for other reasons: one reason to
use them is that they are sometimes more convenient than it is to find a
good place for the non-inline version. Another common reason is that the
thing started out smaller than it eventually became - and the inline just
stuck around.
But if you do things like this for a CONFIG_SMALL, then the convenience
argument obviously isn't true any more, and you'd be a lot better off just
unconditionally making it a real function call.
Function calls aren't all that expensive, especially with FASTCALL() etc
to show that you don't have to follow the common calling conventions.
Right now I think FASTCALL() only matters on x86, but some other
architectures could make it mean "smaller call clobbered list" or similar.
Have you benchmarked with the smaller kernel?
Linus
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