linux-kernel - Re: [PATCH] KVM: VMX: invalidate vpid for invlpg instruction

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Date:	Wed, 05 Sep 2012 23:54:21 +0200
From:	Davidlohr Bueso <dave@....org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>, KVM <kvm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: VMX: invalidate vpid for invlpg instruction

On Mon, 2012-09-03 at 12:11 +0300, Avi Kivity wrote:
> On 09/03/2012 02:27 AM, Davidlohr Bueso wrote:
> > On Fri, 2012-08-31 at 14:37 -0300, Marcelo Tosatti wrote:
> >> On Fri, Aug 31, 2012 at 06:10:48PM +0200, Davidlohr Bueso wrote:
> >> > For processors that support VPIDs we should invalidate the page table entry
> >> > specified by the lineal address. For this purpose add support for individual
> >> > address invalidations.
> >> 
> >> Not necessary - a single context invalidation is performed through
> >> KVM_REQ_TLB_FLUSH.
> > 
> > Since vpid_sync_context() supports both single and all-context vpid
> > invalidations, wouldn't it make sense to also add individual address
> > ones as well, supporting further granularity?
> 
> It might.  Do you have benchmarks supporting this?
> 

I ran two benchmarks: Java Dacapo[1] Sunflow (renders a set of images
using ray tracing) and a vanilla 3.2 kernel build (with 1 job and -j8).

The host configuration is an Intel i7-2635QM (4 cores + HT) with 4Gb RAM
running Linus's latest and only running standard system daemons. For KVM
I disabled EPT.
The guest configuration is a 64bit 4 core 4Gb RAM, running Linux 3.2
(debian) and only running the benchmark.

All results represent the mean of 5 runs, with time(1).

Dacapo without individual addr invvpid:
real   1m25.406s
user   4m59.315s
sys    1m25.406s

Dacapo with individual addr invvpid:
real   1m4.421s
user   3m47.150s
sys    0m1.592s

--

vanilla kernel build without individual addr invvpid:
real   16m42.571s
user   13m28.975s
sys    2m54.487s

vanilla kernel build with individual addr invvpid:
real   15m45.789s
user   12m25.691s
sys    2m44.806s

--

vanilla kernel build (-j8) without individual addr invvpid:
real   10m32.276s
user   33m47.687s
sys    5m37.725s

vanilla kernel build (-j8) with individual addr invvpid:
real   8m29.789s
user   28m12.850s
sys    4m34.353s


In all cases using individual address invalidation outperforms single
context ones regarding wall time. Comments?

[1] http://dacapobench.org/


Thanks,
Davidlohr

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