Re: [Lguest] [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

[Avi Kivity <avi@redhat.com>]

> 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 have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.