linux-kernel - Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE handler

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Message-ID: <20120928181801.GB17449@localhost.localdomain>
Date:	Fri, 28 Sep 2012 14:18:02 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nel.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Jiannan Ouyang <ouyang@...pitt.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE
 handler

> >> 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?
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