linux-kernel - Re: [PATCH v2 5/7] KVM: Introduce PV kick in flush tlb

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Date:	Wed, 4 Jul 2012 23:37:46 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, mingo@...e.hu, avi@...hat.com,
	raghukt@...ux.vnet.ibm.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org, jeremy@...p.org,
	vatsa@...ux.vnet.ibm.com, hpa@...or.com
Subject: Re: [PATCH v2 5/7] KVM: Introduce PV kick in flush tlb

On Tue, Jul 03, 2012 at 01:55:02PM +0530, Nikunj A Dadhania wrote:
> On Tue, 3 Jul 2012 05:07:13 -0300, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> > On Mon, Jun 04, 2012 at 10:38:17AM +0530, Nikunj A. Dadhania wrote:
> > > In place of looping continuously introduce a halt if we do not succeed
> > > after some time.
> > > 
> > > For vcpus that were running an IPI is sent.  In case, it went to sleep
> > > between this, we will be doing flush_on_enter(harmless). But as a
> > > flush IPI was already sent, that will be processed in ipi handler,
> > > this might result into something undesireable, i.e. It might clear the
> > > flush_mask of a new request.
> > > 
> > > So after sending an IPI and waiting for a while, do a halt and wait
> > > for a kick from the last vcpu.
> > > 
> > > Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
> > > Signed-off-by: Nikunj A. Dadhania <nikunj@...ux.vnet.ibm.com>
> > 
> > Again, was it determined that this is necessary from data of 
> > benchmarking on the in-guest-mode/out-guest-mode patch?
> > 
> No, this is more of a fix wrt algo.

Please have numbers for the improvement relative to the previous
patch.

It introduces a dependency, these (pvtlbflush and pvspinlocks) are
separate features. It is useful to switch them on/off individually.

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