Re: [Xen-devel] long latency of domain shutdown

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 08.05.08 14:36 >>>
>> But really, rather than introducing (and fixing) the hack here I'd much
>> prefer a generic solution to the problem, and you didn't say a word on
>> the thoughts I had on that (but in a mail a couple of days ago you
>> indicated you might get around doing something in that area yourself,
>> so I half way implied you may have a mechanism in mind already).
>
>I don't have a very clear plan, except that some kind of continuation
>(basically encoding of how far we got) must be encoded in the page_info
>structure. We should be able to find spare bits for a page which is in this
>in-between state.

Hmm, storing this in page_info seems questionable to me. It'd be at
least 18 bits (on x86-64) that we'd need. I think this rather has to go
into struct vcpu.

But what worries me more is that (obviously) any affected page will
have to have its PGT_validated bit kept clear, which could lead to
undesirable latencies in spin loops on other vcpus waiting for it to
become set. In the worst case this could lead to deadlocks (at least
in the UP case or when multiple vCPU-s of one guest are pinned to
the same physical CPU) afaics. Perhaps this part could indeed be
addressed with a new PGT_* bit, upon which waiters could exit
their spin loops and consider themselves preempted.

Jan


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