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

[H. Peter Anvin]

Alexander van Heukelum wrote:
> 
> That's good to know. I assume this LOCKed bus cycle only occurs
> if the (hidden) segment information is not cached in some way?
> How many segments are typically cached? In particular, does it
> optimize switching between two segments?
> 

Yes, there is a segment descriptor cache (as opposed to the hidden but
architectural segment descriptor *registers*, which the Intel
documentation confusingly call a "cache".)

It is used to optimize switching between a small number of segments, and
was crucial for decent performance on Win9x, which contained a bunch of
16-bit code.

	-hpa
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