Re: [Xen-ia64-devel] PATCH: cleanup of tlbflush

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Mercredi 10 Mai 2006 10:30, Tian, Kevin a écrit :
> From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx]
>
> >Sent: 2006年5月10日 15:29
> >
> >> At least one simple enhancement
> >> we can do is to change syntax of domain_dirty_cpumask. We can
> >> change it to indicate processors that domain is ever running on. Then
> >> update point only happens at creation/destroy/migration, or even
> >> pause/unpause. Though this simple strategy is not fine-grained, we
> >> can still achieve benefit especially when domain is bound.
> >
> >One use of domain_dirty_cpumask is to flush vtlb when a page is
> >ungranted.
> >If this mask is ever set, doing IOs trash the machine.
> >IMHO, this is the next major Xen/ia64 challenge: dealing correctly with
> >granted page.
>
> Not clear about this one. Could you elaborate more? How dose IO cause
> to trash the machine?
[By trashing I mean slowing down].
The current common code calls flush_tlb_mask after ungranting a page.
On xen/ia64, flush_tlb_mask should flush the tlb and the vhpt, which means 
clearing 16MB per vcpu.  This is quiet high.
Unfortunatly, flushing is required for correctness.  The current Isaku 
work-around is to reduce VHPT size (64Kb).  But even with a small size, 
flushing tlb requires an IPI when SMP-g, which is quiet slow.

Tristan.

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