Date: Sun, 18 Aug 2002 17:05:00 -0700 (PDT) From: Julian Elischer <julian@elischer.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Ian Dowse <iedowse@maths.tcd.ie>, Bruce Evans <bde@zeta.org.au>, arch@FreeBSD.ORG Subject: Re: Solving the stack gap issue Message-ID: <Pine.BSF.4.21.0208181659440.42036-100000@InterJet.elischer.org> In-Reply-To: <200208181933.g7IJXYC5072982@apollo.backplane.com>
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On Sun, 18 Aug 2002, Matthew Dillon wrote:
> I would consider this to be more expensive:
>
> proc1()
> {
> struct thread *td = curthread;
> ...
> proc2(td)
> }
>
> proc2(td)
> {
> ...
> }
>
> And this to be less expensive:
>
> proc1()
> {
> proc2();
> }
>
> proc2()
> {
> struct thread *td = curthread;
>
> ... use td several times ...
> }
yes but what about:
proc1()
{
struct thread *td = curthread;
...
someotherfn(td)
proc2(td)
}
proc2(td)
{
...
... use td several times ...
}
vs
proc1()
{
struct thread *td = curthread;
...
someotherfn(td)
proc2()
}
proc2()
{
struct thread *td = curthread;
...
... use td several times ...
}
so that proc1 needs td anyhow..
>
> At least for I386. Ultimately I think this will be generally true on
> any architecture. If a procedure uses 'curthread' multiple times loading
> it into a local at the top of the procedure should be a sufficient
> optimization. Passing td around to dozens or hundreds of procedures
> just for the sake of avoiding accessing 'curthread' is bad design.
>
> -Matt
> Matthew Dillon
> <dillon@backplane.com>
>
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