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SubjectRe: [3/10 PATCH] inline wake_up_bit
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From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Wed, 25 Jun 2008 22:37:58 +0200

> On Wednesday 25 June 2008 18:01, Mikulas Patocka wrote:
> > > Ingo's suggestion to talk to gcc people to remedy
> > > insane call convention sounds as a more workable solution.
> > >
> > > BTW, i386 uses regparm call convention, is similar trick
> > > possible for sparc64?
> >
> > Sparc64 has register windows: it passes arguments in registers, but it
> > must allocate space for that registers. If the call stack is too deep (8
> > levels), the CPU runs out of registers and starts spilling the registers
> > of the function 8-levels-deep to the stack.
> >
> > The stack usage could be reduced to 176 bytes with little work from gcc
> > developers and to 128 bytes with more work (ABI change). If you wanted to
>
> Wow, it's nearly x2 reduction.
>
> ABI change in not a problem for kernel, since it is a "freestanding
> application". Exactly like i386 switched to regparm, which is a different ABI.

Except that nobody has written this code and therefore being about to
use this unimplemented compiler facility to get correctness is not
tenable.


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