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

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>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. 

Thanks,
Kevin

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