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RE: [Xen-devel] Ticket spinlocks and MP guests

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] 
>Sent: 2008年2月15日 16:37
>On 15/2/08 08:27, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>>> Side effect of ticket-based locks, or pv'ed sleeping locks?
>>> -- Keir
>> Side effect about pv'ed sleeping locks, since originally maybe
>> dozens of cycles are used to spin lock while pv'ed locks force
>> hypercall to Xen and may even require owner with another
>> unlock hypercall to notify back?
>You would of course spin for a while and only then sleep. 
>That's a standard
>mutex implementation trick.

I'm not sure how to define 'a while', since even for same critical
section the spin cycles varies at different point. You always risk
adding more overhead than a normal spin loop. But well, it depends
on how frequent forementioned case may occur, and the gain
of pv'ed spinlock may be larger than overhead it causes. 


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