Re: [3/10 PATCH] inline wake_up_bit

Pavel Machek
2008-06-27T12:19:48Z

On Wed 2008-06-25 17:28:38, David Miller wrote:
> 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.

Switch to 32K stack on sparc64, then?

Pavel
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