Messages in this thread | | | Date | Mon, 21 May 2012 16:12:21 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] kvm: optimize ISR lookups |
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On 05/21/2012 04:06 PM, Michael S. Tsirkin wrote: > > I think the reason is __apic_read which now simply copies the registers > out to guest, this code will become less straight-forward if it's not > 1:1. >
It can still be 1:1, just drop the 12 bytes of completely useless padding after each 32-bit datum.
>> And if you look deeper, then you'll notice that _ALL_ APIC registers >> are on a 16 byte boundary (thanks Peter for pointing that out). >> >> So it's even more silly to have a 1:1 representation instead of >> implementing the default emulated apic_read/write functions to access >> (offset >> 2). >> >> And of course, that design decision causes lookups to be slow. > > Yes, it might be one of the reasons why my patch helps so > much: it adds a cache in front of this data structure. >
Well, *fix the fscking data structure first*.
> > So what you propose is in fact to rework apic registers at least for > ISR,IRR,TMR to use a bitmap. > I am fine with this suggestion but would like some feedback from kvm > maintainers on where they want to go before I spend time on that. >
This should be a 20-minute hack.
-hpa
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