Re: [3/10 PATCH] inline wake_up_bit

Denys Vlasenko
2008-06-26T03:36:11Z

On Thursday 26 June 2008 02:28, David Miller wrote:
> From: Denys Vlasenko <vda.linux@googlemail.com>
> Date: Wed, 25 Jun 2008 22:37:58 +0200
> > > 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.

Inlining everything is even less tenable. Why architectures which do not
require 128+ bytes of stack for every function call should suffer?

I am all for fixing code where there are extra useless levels of calls,
but in this example I pointed out that patch adds inlines too liberally.
Do you agree that blowing up every wake_up_bit() into half a dozen
or more C lines is not what we want?
--
vda