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Date: Fri, 28 Sep 2012 14:18:02 -0400
From: Konrad Rzeszutek Wilk <konrad@kernel.org>
To: Avi Kivity <avi@redhat.com>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Jiannan Ouyang <ouyang@cs.pitt.edu>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Srikar <srikar@linux.vnet.ibm.com>,
        "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
        KVM <kvm@vger.kernel.org>, chegu vinod <chegu_vinod@hp.com>,
        "Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
        Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE
 handler
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> >> PLE:
> >> - works for unmodified / non-Linux guests
> >> - works for all types of spins (e.g. smp_call_function*())
> >> - utilizes an existing hardware interface (PAUSE instruction) so likely
> >> more robust compared to a software interface
> >>
> >> PV:
> >> - has more information, so it can perform better
> > 
> > Should we also consider that we always have an edge here for non-PLE
> > machine?
> 
> True.  The deployment share for these is decreasing rapidly though.  I
> hate optimizing for obsolete hardware.

Keep in mind that the patchset that Jeremy provided also cleans (remove)
parts of the pv spinlock code. It removes the various spin_lock,
spin_unlock, etc that touch paravirt code. Instead the pv code is only
in the slowpath. And if you don't compile with CONFIG_PARAVIRT_SPINLOCK
the end code is the same as it is now.

On a different subject-  I am curious whether the Haswell new locking
instructions (the transactional ones?) can be put in usage for the slow
case?