Steve, > On Mon, 17 Nov 2008, Linus Torvalds wrote: > > > > I do wonder just _what_ it is that causes the stack frames to be so > > horrid. For example, you have > > > > 18) 8896 160 .kmem_cache_alloc+0xfc/0x140 > > > > and I'm looking at my x86-64 compile, and it has a stack frame of just 8 > > bytes (!) for local variables plus the save/restore area (which looks like > > three registers plus frame pointer plus return address). IOW, if I'm > > looking at the code right (so big caveat: I did _not_ do a real stack > > dump!) the x86-64 stack cost for that same function is on the order of 48 > > bytes. Not 160. > > Out of curiosity, I just ran stack_trace on the latest version of git > (pulled sometime today) and ran it on my x86_64. > > I have SLUB and SLUB debug defined, and here's what I found: > > 11) 3592 64 kmem_cache_alloc+0x64/0xa3 > > 64 bytes, still much lower than the 160 of PPC64.
The ppc64 ABI has a minimum stack frame of 112 bytes, due to having an area for called functions to store their parameters (64 bytes) plus 6 slots for saving stuff and for the compiler and linker to use if they need to. That's before any local variables are allocated. The ppc32 ABI has a minimum stack frame of 16 bytes, which is much nicer, at the expense of a much more complicated va_arg(). Paul. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
