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xen-ia64-devel
Re: [Xen-ia64-devel] RE: [PATCH]: disable handling of legacy privified i
Le Lundi 20 Mars 2006 17:08, Magenheimer, Dan (HP Labs Fort Collins) a écrit :
Hi,
[...]
> Is there a reason you are proposing to change the design
> of hyperprivops?
No, I don't want to change the design, I am just trying to understand it
fully.
> I realize that the few hyperprivops you
> just implemented are a bit ugly because it is necessary
> to save/restore virtual psr.ic and virtual psr.i, but
> these were never previously implemented as hyperprivops
> because they were relatively low frequency. The virtual
> psr.ic trick works nicely for the high frequency ones.
Sure.
> Do you think the pl=2 approach will yield a significant
> performance advantage? Or is there some other reason?
I don't see immediat performance advantage.
I was just thinking about privileged operations.
We all agree these are slow and have a bad impact on D cache.
Their handling also suppose that I=D, because the bundle is read using ld8.
We agree this is not a problem with para-virtualized linux; this is more or
less a theorical issue. But it makes vcpu_translate strange.
Now suppose we'd like to fix this issue. We can either fetch the opcode using
a manually translated mpa. This would be slow. Maybe we could make
measures. Or we can replace the pivop by a break on the fly. To do this, we
must be able to catch break insn and have enough room in the iim space.
This was just a thinking, I have written it down.
Tristan.
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