On 03/30/2011 03:26 PM, Gleb Natapov wrote:
On Wed, Mar 30, 2011 at 02:48:28PM +0200, Gleb Natapov wrote:
> On Wed, Mar 30, 2011 at 02:17:55PM +0200, Avi Kivity wrote:
> > On 03/30/2011 01:43 PM, Gleb Natapov wrote:
> > >After reboot perf started to work. I ran modified emulator.flat unit
> > >test. It was modified to run test_cmps() in an endless loop.
> > >
> > >Without patch:
> > >1.71% qemu-system-x86 [kvm] [k] x86_emulate_instruction
> > >1.51% qemu-system-x86 [kvm] [k] x86_emulate_instruction
> > >1.68% qemu-system-x86 [kvm] [k] x86_emulate_instruction
> > >
> > >With patch:
> > >0.84% qemu-system-x86 [kvm] [k] x86_emulate_instruction
> > >0.96% qemu-system-x86 [kvm] [k] x86_emulate_instruction
> > >0.89% qemu-system-x86 [kvm] [k] x86_emulate_instruction
> > >
> >
> > The cause might be kvm_rip_write() using vmwrite. Can you use perf
> > to see where the hits are in x86_emulate_instruction?
> >
> > If that's the case, we may be able to do local optimizations to
> > kvm_rip_write(), kvm_set_rflags(), and toggle_interruptiblity()
> > instead of this global change.
> >
> I can leave copying there and eliminate only kvm_rip_write and see
> perf data.
>
1.75% qemu-system-x86 [kvm] [k] x86_emulate_instruction
1.60% qemu-system-x86 [kvm] [k] x86_emulate_instruction
1.42% qemu-system-x86 [kvm] [k] x86_emulate_instruction
This is with copy in place, but those are under if (writeback):
toggle_interruptibility(vcpu,
vcpu->arch.emulate_ctxt.interruptibility);
kvm_set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
kvm_make_request(KVM_REQ_EVENT, vcpu);
vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
It's wierd. Do you get perf hits in the copying?
Copying a couple of hot cache lines shouldn't take any measurable time
compared to a heavyweight exit.
--
error compiling committee.c: too many arguments to function
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