Re: measuring and/or dealing with "idleness" and variable frequency

[Rick Jones <rick.jones2@hp.com>]

On 06/10/2013 03:39 PM, Rick Jones wrote:
> On 06/10/2013 03:33 PM, David Ahern wrote:
>> On 6/10/13 4:28 PM, Rick Jones wrote:
>>>> I think I could get what I want from that - assuming I could get
>>>> that to
>>>> a kernel I can use in my test env, but am guessing it is rather more
>>>> than I"m looking for at the moment.  I'm wondering if there might be a
>>>> simpler way to go - just get the idle loop to keep looping rather than
>>>> halt (?) the thread, so there would still be cycle events in the PMU?
>>>> (And perhaps set the system to a static, high-performance mode to avoid
>>>> frequency changes and maybe even disable HT?)
>>>
>>> Or, after having found
>>> https://www.kernel.org/doc/Documentation/kernel-parameters.txt, perhaps
>>> idle=poll?
>>
>> Yes, that should turn the server into a power-sucking space heater and
>> keep the cycles counter firing.
>
> Excellent - I can live with the server being a power-sucking space
> heater for the duration of my profiling.  Heck, many of the servers I
> used to work on were always power-sucking space heaters :)

Just for the archives and anyone looking to go "space heater" in the 
future - it is a Good Idea (tm) to disable hyper threads (at least with 
this sort of hyper threading in E5-2670 processors) or you can have what 
I presume are two HT's battling one another in the idle loop.

rick jones