[Xen-devel] Re: [RFC, PATCH 16/24] i386 Vmi io header

[ebiederm@xxxxxxxxxxxx (Eric W. Biederman)]

Zachary Amsden <zach@xxxxxxxxxx> writes:

> Move I/O instruction building to the sub-arch layer.  Some very crafty
> but esoteric macros are used here to get optimized native instructions
> for port I/O in Linux be writing raw instruction strings.  Adding a
> wrapper layer here is fairly easy, and makes the full range of I/O
> instructions available to the VMI interface.
>
> Also, slowing down I/O is not a useful operation in a VM, so there
> is a VMI call specifically to allow making it a NOP.  I could find
> no place where SLOW_IO_BY_JUMPING is still used, and consider it
> obsoleted.  Even on older 386 systems, the I/O delay approximation
> by touching the extra page register is likely to better.

This sounds like a prime candidate for the alternate instruction interfaces
and I don't see that being used here.

Eric

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