From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Date: Thu, 21 Aug 2008 13:31:46 +0000
Subject: Re: [PATCH 4/4] kvmppc: convert wrteei to wrtee as kvm guest optimization
Message-Id: <48AD6E42.6060406@linux.vnet.ibm.com>
List-Id: <kvm-ppc.vger.kernel.org>
References: <1219142204-12044-1-git-send-email-ehrhardt@linux.vnet.ibm.com>
	<1219142204-12044-5-git-send-email-ehrhardt@linux.vnet.ibm.com>
	<200808191342.29918.arnd@arndb.de>
	<48AC13E5.5010503@linux.vnet.ibm.com>
	<1219257000.14362.90.camel@localhost.localdomain>
	<1219258333.26429.29.camel@jdub.homelinux.org>
	<1219259211.14362.94.camel@localhost.localdomain>
	<20080820151848.69cb8f16@zod.rchland.ibm.com>
In-Reply-To: <20080820151848.69cb8f16@zod.rchland.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
To: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Cc: linuxppc-dev@ozlabs.org, Arnd Bergmann <arnd@arndb.de>, kvm-ppc@vger.kernel.org, Hollis Blanchard <hollisb@us.ibm.com>

Josh Boyer wrote:
> On Wed, 20 Aug 2008 14:06:51 -0500
> Hollis Blanchard <hollisb@us.ibm.com> wrote: =20
>  =20
>>>>> To be honest I unfortunately don't know how big the impact for=20
>>>>> non-virtualized systems is. I would like to test it, but without=20
>>>>> hardware performance counters on the core I have I'm not sure (yet)
>>>>> how=20
>>>>> to measure that in a good way - any suggestion welcome.
>>>>>          =20
>>>> I don't see why we need performance counters. Can't we just compare any
>>>> bare metal benchmark results with the patch both applied and not?
>>>>        =20
>>> Do you know of one that causes a large amount of
>>> local_irq_{disable,enable}s to be called?
>>>      =20
>> I think *every* workload causes a large number of
>> local_irq_{disable,enable} calls... :)
>>    =20
>
> Well, sure.  I was just going for "test the change as specifically as
> possible."  One could write a module that did X number of
> disable/enable pairs and reported the timebase at start and end to
> compare.  X could even be a module parameter.  Just to try and
> eliminate noise or whatever from the testing.
>
> /me shrugs.
>
> josh
>  =20
yeah I thought of something like that too, because I expect the=20
difference to be very small.
Instead of a module I wanted to put this somewhere prior to the kernel=20
mounting root-fs to avoid interferences from whatever userspace is doing=20
(e.g. causing  thousands of interrupts come back while the module=20
perform that test.).
Eventually we need a synthetic benchmark like that AND a check how it=20
affects a common system to be sure.


--=20

Gr=FCsse / regards,=20
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization