From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: lock in vhpet
Date: Mon, 23 Apr 2012 09:22:46 +0100
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To: "Zhang, Yang Z" <yang.z.zhang@intel.com>, Jan Beulich <JBeulich@suse.com>, Tim Deegan <tim@xen.org>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Andres Lagar-Cavilla <andres@lagarcavilla.org>
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On 23/04/2012 09:15, "Zhang, Yang Z" <yang.z.zhang@intel.com> wrote:

>>> 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?
>> 
> Right. Using rwlock would make more sense.

Interested to see if it would improve performance. My guess would be no.

 -- Keir