linux/arch/x86
Jeremy Fitzhardinge ecb93d1ccd x86/paravirt: add register-saving thunks to reduce caller register pressure
Impact: Optimization

One of the problems with inserting a pile of C calls where previously
there were none is that the register pressure is greatly increased.
The C calling convention says that the caller must expect a certain
set of registers may be trashed by the callee, and that the callee can
use those registers without restriction.  This includes the function
argument registers, and several others.

This patch seeks to alleviate this pressure by introducing wrapper
thunks that will do the register saving/restoring, so that the
callsite doesn't need to worry about it, but the callee function can
be conventional compiler-generated code.  In many cases (particularly
performance-sensitive cases) the callee will be in assembler anyway,
and need not use the compiler's calling convention.

Standard calling convention is:
	 arguments	    return	scratch
x86-32	 eax edx ecx	    eax		?
x86-64	 rdi rsi rdx rcx    rax		r8 r9 r10 r11

The thunk preserves all argument and scratch registers.  The return
register is not preserved, and is available as a scratch register for
unwrapped callee code (and of course the return value).

Wrapped function pointers are themselves wrapped in a struct
paravirt_callee_save structure, in order to get some warning from the
compiler when functions with mismatched calling conventions are used.

The most common paravirt ops, both statically and dynamically, are
interrupt enable/disable/save/restore, so handle them first.  This is
particularly easy since their calls are handled specially anyway.

XXX Deal with VMI.  What's their calling convention?

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2009-01-30 14:51:45 -08:00
..
boot
configs eeprom: More consistent symbol names 2009-01-26 21:19:57 +01:00
crypto
ia32 x86-64: Move kernelstack from PDA to per-cpu. 2009-01-19 00:38:58 +09:00
include/asm x86/paravirt: add register-saving thunks to reduce caller register pressure 2009-01-30 14:51:45 -08:00
kernel x86/paravirt: add register-saving thunks to reduce caller register pressure 2009-01-30 14:51:45 -08:00
kvm
lguest x86/paravirt: add register-saving thunks to reduce caller register pressure 2009-01-30 14:51:45 -08:00
lib x86: use early clobbers in usercopy*.c 2009-01-21 09:43:17 +01:00
mach-default
mach-generic
mach-rdc321x
mach-voyager x86: initialize per-cpu GDT segment in per-cpu setup 2009-01-27 12:56:48 +09:00
math-emu
mm Merge branch 'tj-percpu' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc into core/percpu 2009-01-27 12:03:24 +01:00
oprofile
pci x86 PAT: consolidate old memtype new memtype check into a function 2009-01-13 19:13:00 +01:00
power
vdso
video
xen x86/paravirt: add register-saving thunks to reduce caller register pressure 2009-01-30 14:51:45 -08:00
Kconfig x86: make Voyager use x86 per-cpu setup. 2009-01-27 12:56:48 +09:00
Kconfig.cpu x86: make x86_32 use tlb_64.c, build fix, clean up X86_L1_CACHE_BYTES 2009-01-21 11:17:11 +01:00
Kconfig.debug
Makefile
Makefile_32.cpu