Re: [PATCH] KVM: emulator: do not needlesly sync registers from emulator ctxt to vcpu

[Gleb Natapov <gleb@redhat.com>]

On Wed, Mar 30, 2011 at 03:41:09PM +0200, Avi Kivity wrote:
> On 03/30/2011 03:36 PM, Gleb Natapov wrote:
> >>
> >>  It's wierd.  Do you get perf hits in the copying?
> >>
> >How can I check. The memcpy is inlined.
> >
> 
> perf annotate x86_emulate_instruction
> 
> (newer perf allows you to get there interactively from 'perf report')
> 
> >>  Copying a couple of hot cache lines shouldn't take any measurable
Ah, forgot about it:

First one:
27.71 :           1179f:       f3 a5                   rep movsl %ds:(%rsi),%es:(%rdi)

Second one:
32.68 :           11888:       f3 a5                   rep movsl %ds:(%rsi),%es:(%rdi)

> >>  time compared to a heavyweight exit.
> >>
> >The whole function takes only 1.5% CPU. Perf measures how much this
> >function become faster and heavyweight exit is not part of the function.
> 
> It's still relative to exit cost.  If the total exit was 2 us, then
> a 1% decrease in cost translates to 40 ns.
> 
> (well, that's not unlikely for a 256 byte memcpy, but let's be sure).
> 
> -- 
> error compiling committee.c: too many arguments to function

--
			Gleb.