Messages in this thread | | | Date | Mon, 25 Jul 2011 10:42:15 +0300 | From | Avi Kivity <> | Subject | Re: [RFC] syscall calling convention, stts/clts, and xstate latency |
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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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