Commit 54cfdb3e authored Mar 27, 2014 by Paolo Bonzini

KVM: emulate: speed up emulated moves

We can just blindly move all 16 bytes of ctxt->src's value to ctxt->dst.
write_register_operand will take care of writing only the lower bytes.

Avoiding a call to memcpy (the compiler optimizes it out) gains about
200 cycles on kvm-unit-tests for register-to-register moves, and makes
them about as fast as arithmetic instructions.

We could perhaps get a larger speedup by moving all instructions _except_
moves out of x86_emulate_insn, removing opcode_len, and replacing the
switch statement with an inlined em_mov.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent d40a6898

arch/x86/include/asm/kvm_emulate.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -233,7 +233,7 @@ struct operand {
		union {
		unsigned long val;
		u64 val64;
		char valptr[sizeof(unsigned long) + 2];
		char valptr[sizeof(sse128_t)];
		sse128_t vec_val;
		u64 mm_val;
		void *data;

arch/x86/kvm/emulate.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -2990,7 +2990,7 @@ static int em_rdpmc(struct x86_emulate_ctxt *ctxt)

		static int em_mov(struct x86_emulate_ctxt *ctxt)
		{
		memcpy(ctxt->dst.valptr, ctxt->src.valptr, ctxt->op_bytes);
		memcpy(ctxt->dst.valptr, ctxt->src.valptr, sizeof(ctxt->src.valptr));
		return X86EMUL_CONTINUE;
		}