Re: [RFC] syscall calling convention, stts/clts, and xstate latency

[Avi Kivity <avi@redhat.com>]

On 07/25/2011 12:15 AM, Ingo Molnar wrote:
> >  All of this makes me think that, at least on Sandy Bridge, lazy
> >  xstate saving is a bad optimization -- if the cache is being nice,
> >  save/restore is faster than twiddling the TS bit.  And the cost of
> >  the trap when TS is set blows everything else away.
>
> Interesting. Mind cooking up a delazying patch and measure it on
> native as well? KVM generally makes exceptions more expensive, so the
> effect of lazy exceptions might be less on native.

While this is true in general, kvm will trap #NM only after a host 
context switch or an exit to host userspace.  These are supposedly rare 
so you won't see them a lot, especially in a benchmark scenario with 
just one guest.

("host context switch" includes switching to the idle thread when the 
guest executes HLT, something I tried to optimize in the past but it 
proved too difficult for the gain)

-- 
error compiling committee.c: too many arguments to function