Messages in this thread Patch in this message | | | From | Paolo Bonzini <> | Subject | [RFC PATCH 5/5] KVM: x86: speed up emulated moves | Date | Thu, 27 Mar 2014 12:30:38 +0100 |
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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 50 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> --- arch/x86/include/asm/kvm_emulate.h | 2 +- arch/x86/kvm/emulate.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h index 24ec1216596e..f7b1e45eb753 100644 --- a/arch/x86/include/asm/kvm_emulate.h +++ b/arch/x86/include/asm/kvm_emulate.h @@ -232,7 +232,7 @@ 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; diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 94974055d906..4a3584d419e5 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -2955,7 +2955,7 @@ 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; } -- 1.8.3.1
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