Re: [PATCH 0/7] Streamline arithmetic instruction emulation

Gleb Natapov
2012-12-23T09:47:17Z

On Sat, Dec 22, 2012 at 02:26:50PM +0200, Avi Kivity wrote:
> The current arithmetic instruction emulation is fairly clumsy: after
> decode, each instruction gets a switch (size), and for every size
> we fetch the operands, prepare flags, emulate the instruction, then store
> back the flags and operands.
>
> This patchset simplifies things by moving everything into common code
> except the instruction itself. All the pre- and post- processing is
> coded just once. The per-instrution code looks like:
>
> add %bl, %al
> ret
>
> add %bx, %ax
> ret
>
> add %ebx, %eax
> ret
>
> add %rbx, %rax
> ret
>
> The savings in size, for the ten instructions converted in this patchset,
> are fairly large:
>
> text data bss dec hex filename
> 63724 0 0 63724 f8ec arch/x86/kvm/emulate.o.before
> 61268 0 0 61268 ef54 arch/x86/kvm/emulate.o.after
>
> - around 2500 bytes.
>
> Avi Kivity (7):
> KVM: x86 emulator: framework for streamlining arithmetic opcodes
> KVM: x86 emulator: Support for declaring single operand fastops
> KVM: x86 emulator: introduce NoWrite flag
> KVM: x86 emulator: mark CMP, CMPS, SCAS, TEST as NoWrite
> KVM: x86 emulator: convert NOT, NEG to fastop
> KVM: x86 emulator: add macros for defining 2-operand fastop emulation
> KVM: x86 emulator: convert basic ALU ops to fastop
>
> arch/x86/kvm/emulate.c | 215 +++++++++++++++++++++++++++----------------------
> 1 file changed, 120 insertions(+), 95 deletions(-)
>
Looks good to me.

--
Gleb.