Messages in this thread |  | | | Date | Mon, 25 Jul 2011 09:54:22 +0200 | | From | Ingo Molnar <> | | Subject | Re: [RFC] syscall calling convention, stts/clts, and xstate latency |
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* Avi Kivity <avi@redhat.com> wrote:
> 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)
Yeah - but this was a fair thing to test before Andy embarks on something more ambitious on the native side.
Thanks,
Ingo
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