linux-kernel - Re: [PATCH v2 4/6] KVM: VMX: dynamise PLE window

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Message-ID: <20140821114739.GC20546@potion.brq.redhat.com>
Date:	Thu, 21 Aug 2014 13:47:40 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gleb Natapov <gleb@...nel.org>,
	Raghavendra KT <raghavendra.kt@...ux.vnet.ibm.com>,
	Vinod Chegu <chegu_vinod@...com>,
	Hui-Zhi <hui-zhi.zhao@...com>,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH v2 4/6] KVM: VMX: dynamise PLE window

2014-08-21 10:24+0200, Paolo Bonzini:
> Il 20/08/2014 22:53, Radim Krčmář ha scritto:
> > +static void update_ple_window_actual_max(void)
> > +{
> > +	ple_window_actual_max =
> > +			__shrink_ple_window(max(ple_window_max, ple_window),
> 
> Why the max() here?

To have ple_window act as a ple_window_min as well.
(When we are already preventing most stupid choices.)

And it's cheap ... I can add comment to this function :)

> > +			                    ple_window_grow, INT_MIN);
> 
> This should be 0 (in fact you can probably make everything unsigned now
> that you've sorted out the overflows).

Not in v2:
  val = min(vmx->ple_window, ple_window_actual_max);
  val += ple_window_grow;
  vmx->ple_window = val;
so we need to dip below zero to allow all possible grows.

(I'm not sure if anyone is ever going to use the additive option, so
 getting rid of it is also a valid choice -- code would be nicer.)
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