On Tue, Jan 30, 2007 at 09:46:04AM +0800, Xu, Anthony wrote:
> Isaku Yamahata write on 2007年1月29日 18:29:
> >
> > How about the following example?
> > For simplicity, we consider only local_flush_tlb_all().
> > (The similar argument can be applied to vcpu_vhpt_flush())
> >
> > suppose domM has two vcpus, vcpu0, vcpu1.
> > domN has one vcpu, vcpu2.
> >
> > - case 1
> > vcpu0 and vcpu1 are running on same pcpu.
> > vcpu0 runs.
> > context switch <<<< local_flush_tlb_all() is necessry here
> > vcpu1 runs.
> >
> > - case 2
> > vcpu0, vcpu1 and vcpu2 are running on the same pcpu
> > vcpu0 runs
> > context switch
> > vcpu2 runs
> > vcpu2 issues local_tlb_flush().
> > context switch <<< local_flush_tlb_all() can be skipped.
> I can understand this. Yes, this local_flush_tlb_all can be skipped,
> But it is because vcpu2 issues local_tlb_flush.
> My question is why we need new_tlbflush_clock_period?
Because the counter is finite.
If we can ignore conter overflow, we can check only which counter
is bigger.
But when overflow comes in (i.e. counter == 0 after increment),
things become complicated. It's the reason of new_tlbflush_clock_period.
Probably another approach to address overflow is to use signed comparison
like Linux jiffies time_after().
But we can't assume the distance between two conters is near enough.
> > You can confirm its effect by the perf-counters,
> > tlbflush_clock_cswitch_skip, flush_vtlb_for_context_switch and
> > tlbflush_clock_cswitch_purge.
> > Please note that local_flush_tlb_all() (or vcpu_vhpt_flush()) is
> > called everytime grant table unmapping without tlb insert tracking
> Currently, grant table unmapping did not purge any thing,
> Because in flush_tlb_mask(current->domain->domain_dirty_cpumask);
> Domain_dirty_cpumask is always 0.
It does.
destroy_grant_host_mapping()
=> domain_page_flush_and_put()
=> domain_flush_vtalb_all()
or
domain_flush_vtlb_track_entry()
Yes, this execution path is somewhat confusing.
I think that flush_tlb_mask(current->domain->domain_dirty_cpumask)
should be replaced with something like arch_flush_tlb(current).
--
yamahata
_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel
|
Home