Re: [Xen-devel] lock in vhpet

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.12 at 09:36, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
> The p2m lock in __get_gfn_type_access() is the culprit. Here is the profiling 
> data with 10 seconds:
> 
> (XEN) p2m_lock 1 lock:
> (XEN)   lock:      190733(00000000:14CE5726), block:       
> 67159(00000007:6AAA53F3)
> 
> Those data is collected when win8 guest(16 vcpus) is idle. 16 VCPUs blocked 
> 30 seconds with 10 sec's profiling. It means 18% of cpu cycle is waiting for 
> the p2m lock. And those data only for idle guest. The impaction is more 
> seriously when run some workload inside guest. 
> I noticed that this change was adding by cs 24770. And before it, we don't 
> require the p2m lock in _get_gfn_type_access. So is this lock really 
> necessary?

Or shouldn't such a lock frequently taken on a read path be an rwlock
instead?

Jan


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