Messages in this thread | | | From | Denys Vlasenko <> | Subject | Re: [3/10 PATCH] inline wake_up_bit | Date | Thu, 26 Jun 2008 05:35:59 +0200 |
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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
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