[PATCH 06/25] KVM: emulate: speed up emulated moves

From: Paolo Bonzini
Date: Mon Jun 09 2014 - 09:03:54 EST


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@xxxxxxxxxx>
---
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 ffa2671a7f2f..46725e8aa8cb 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 4c2ae824e89e..5f902d40740c 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2983,7 +2983,7 @@ 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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