[PATCH 4/4] kvmppc: convert wrteei to wrtee as kvm guest optimization

Christian Ehrhardt ehrhardt at linux.vnet.ibm.com
Thu Aug 21 23:31:46 EST 2008

Josh Boyer wrote:
> On Wed, 20 Aug 2008 14:06:51 -0500
> Hollis Blanchard <hollisb at us.ibm.com> wrote:  
>>>>> To be honest I unfortunately don't know how big the impact for 
>>>>> non-virtualized systems is. I would like to test it, but without 
>>>>> hardware performance counters on the core I have I'm not sure (yet)
>>>>> how 
>>>>> to measure that in a good way - any suggestion welcome.
>>>> 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?
>>> Do you know of one that causes a large amount of
>>> local_irq_{disable,enable}s to be called?
>> I think *every* workload causes a large number of
>> local_irq_{disable,enable} calls... :)
> 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
yeah I thought of something like that too, because I expect the 
difference to be very small.
Instead of a module I wanted to put this somewhere prior to the kernel 
mounting root-fs to avoid interferences from whatever userspace is doing 
(e.g. causing  thousands of interrupts come back while the module 
perform that test.).
Eventually we need a synthetic benchmark like that AND a check how it 
affects a common system to be sure.


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

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