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

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

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 :)

happy benchmarking,

rick jones

Interestingly enough, on the old Centrino-based laptop where I've tried 
it (on AC power), read_hpet has gone away completely.  I'd noticed that 
was visible in several examples in the tutorial on the wiki, but it 
wasn't explained.