Messages in this thread | | | Date | Wed, 26 Nov 2008 23:50:20 +0200 | From | Avi Kivity <> | Subject | Re: [Lguest] [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes |
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Avi Kivity wrote: > >> Here is a prototype patch of the compressed IRQ stubs -- this patch >> compresses them down to 7 stubs per 32-byte cache line (or part of cache >> line) at the expense of a back-to-back jmp which has the potential of >> being ugly on some pipelines (we can only get 4 stubs into 32 bytes >> without that). >> > > You could actually get 4-byte stubs, using a 16-bit call (66 e8 ww > ww). But it would be slower, since we won't be pairing it with a ret. > > I suspect we could get it down to three bytes, by sharing the last > byte of the four-byte call sequence with the first byte of the next: > > 66 e8 ff 66 e8 fc 66 e8 f9 66 e8 f6 ... > > Every three bytes a new stub begins; it's a four-byte call to offset > 0x6703 relative to the beginning of the first stub. > > Can anyone better 24 bits/stub?
I actually got it down to 16 bits: use a 16-bit code segment, so you can drop the address size override:
e8 ff e8 fd e8 fb ...
of course the common code has to jump back to a 32-bit code segment.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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