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



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