From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Date: Mon, 10 Nov 2008 08:28:41 +0000
Subject: Re: Exit timing - results online
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To: kvm-ppc@vger.kernel.org

Hollis Blanchard wrote:
> On Thu, 2008-11-06 at 12:25 +0100, Christian Ehrhardt wrote:
>  =20
>> Hi,
>> I just added the following page to our wiki based online documentation=20
>> to show some numbers on kvmppc as of today.
>> You can find that page at thew wiki entry:
>>   PowerPC_Exittimings=20
>> <http://kvm.qumranet.com/kvmwiki/PowerPC_Exittimings> - an overview of=20
>> workload dependent overhead on non hardware assisted powerpc virtualizat=
ion
>>   (http://kvm.qumranet.com/kvmwiki/PowerPC_Exittimings)
>>    =20
>
> Very interesting; thanks for putting these numbers together Christian.
>
> I'm interested by the instruction emulation, which shows up as the
> highest cost in every workload. That suggests that even small
> improvements to the emulation path, such as using a better lookup than
> nested switch statements, could have a significant effect on throughput.
>
> It's also interesting that the average is really close to the minimum,
> but the standard deviation is huge. That suggests that the vast majority
> of exits take the minimum amount of time, but a few exits take a *ton*
> of time. Looking through the set of instructions we emulate on 440, it
> looks like the only even slightly sophisticated ones are rfi, tlbwe, and
> tlbsx...
>
>  =20
Yeah I extended my patch a bit to now account several different=20
subcategories of the emulation.
One issue was that a idling guest setting MSR[WE] came via the emulation=20
path and recorded all the time a kvm_block waited until there was work=20
for the cpu.

I updated the numbers on the wiki page on Friday.

--=20

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