[tesla-dev] Turbo Mode Support for Solaris

[Eric Saxe]

Mark Haywood wrote:
>
>> I guess we already discussed this issue before?
>> Turbo mode is exported as P0 = marked frequency + 1Mhz,
>> but allow the processors to run faster so that the performance can
>> be improved up to 20%. Average CPU frequency is doable by the
>> hardware feedback mechanism.
>>   
>>     
>
> I think that Vinay was asking Jim about the RFE that he added to 
> http://www.opensolaris.org/os/project/tesla/Work/Powertop/
>
> As I think you and I discussed on the alias earlier, the average CPU 
> frequency while in P0 can be determined by strategically placing 
> APERF/MPERF value dtrace probes when transitioning to and from P0. At 
> least that would be the first thing I'd try ...
>   
We were chatting about this yesterday, and I was wondering what happens 
if we stay at P0 long enough to where APERF/MPERF could wrap? Is that a 
concern...or is the time it would take the counters to wrap sufficiently 
long? I haven't looked in detail yet, but I was also wondering if 
there's a way to explicitly reset the counters at the beginning of a 
sampling interval to maximize the time-to-wrap (if it is short).

Thanks,
-Eric