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

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

On 06/10/2013 01:34 PM, Rick Jones wrote:
> On 06/08/2013 08:21 PM, David Ahern wrote:
>> On 6/6/13 11:46 AM, Rick Jones wrote:
>>> I am coming to "perf" (record -e cycles and report) from an old-time
>>> background where one could see the "idle routine" in a profile and know
>>> how "idle" (in terms of classic reporting a la top) a CPU was.  Back
>>> then the frequency was fixed, the idle loop was always "running" when
>>> the CPU was idle and there were no hardware threads.  Life was simple
>>> and good.
>>
>> You could use the scheduling events or context-switches to know when a
>> CPU is idle. Idle time for a CPU is one of the stats my perf-timehist
>> command shows. I just dumped it to LKML:
>>     https://lkml.org/lkml/2013/6/7/656
>>
>> It's an RFC from an inclusion upstream but it has been used for over 2
>> years.
>
> 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?

rick jones