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Message-ID: <1348841585.3292.76.camel@twins>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler
From: Peter Zijlstra <peterz@infradead.org>
To: habanero@linux.vnet.ibm.com
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Avi Kivity <avi@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
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        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
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Date: Fri, 28 Sep 2012 16:13:05 +0200
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On Fri, 2012-09-28 at 06:40 -0500, Andrew Theurer wrote:
> It will be interesting to see how this behaves with a very high lock
> activity in a guest.  Once the scheduler defers preemption, is it for
> a
> fixed amount of time, or does it know to cut the deferral short as
> soon
> as the lock depth is reduced [by x]? 

Since the locks live in a guest/userspace, we don't even know they're
held at all, let alone when state changes.

Also, afaik PLE simply exits the guest whenever you do a busy-wait,
there's no guarantee its due to a lock at all, we could be waiting for a
'virtual' hardware resource or whatnot.