Re: Exit timing - results online

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Hollis Blanchard wrote:
> On Thu, 2008-11-06 at 12:25 +0100, Christian Ehrhardt wrote:
>   
>> Hi,
>> I just added the following page to our wiki based online documentation 
>> to show some numbers on kvmppc as of today.
>> You can find that page at thew wiki entry:
>>   PowerPC_Exittimings 
>> <http://kvm.qumranet.com/kvmwiki/PowerPC_Exittimings> - an overview of 
>> workload dependent overhead on non hardware assisted powerpc virtualization
>>   (http://kvm.qumranet.com/kvmwiki/PowerPC_Exittimings)
>>     
>
> 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...
>
>   
Yeah I extended my patch a bit to now account several different 
subcategories of the emulation.
One issue was that a idling guest setting MSR[WE] came via the emulation 
path and recorded all the time a kvm_block waited until there was work 
for the cpu.

I updated the numbers on the wiki page on Friday.

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization