[okl4-developer] PMCs

[David Leimbach]

Stefan,

Intel Nehalem changes it's clock frequency in 133MHz increments as a way to do power management.  I believe you can even halt the CPU and resume it without messing things up too badly in their architecture.  I also don't think that's a new idea, but I forget who did it first.

Dave
On Jan 7, 2010, at 2:20 AM, Stefan M. Petters wrote:

> Hi,
> 
> both correct. However, you can usually access the BIOS at boot time. The CPU core frequency is not going to change (unless you do DFS, clock gating, etc).
> Only thing left on PC style architecture is that the BIOS might decide to scale down regardless, if it deems the CPU is getting too hot.
> 
>     Stefan.
> 
> Frank Kaiser wrote:
>> 
>> XScale is not a x86/IA32 architecture.
>> On a system running OKL4 you cannot access any BIOS functions, because they are all real mode implementations while OKL4 is running in protected mode.
>>  
>> Frank
>> From: developer-bounces at okl4.org [mailto:developer-bounces at okl4.org] On Behalf Of Stefan M. Petters
>> Sent: Thursday, January 07, 2010 10:58 AM
>> To: Frank Kaiser
>> Cc: Peter Nguyen; developer
>> Subject: Re: [okl4-developer] PMCs
>>  
>> Hi,
>> 
>> Frank Kaiser wrote:
>> Hello
>>  
>> Most of modern x86 processors provide the TSC for performance monitoring. According to what I remember from INTEL’s x86 architecture documentation it is guaranteed that the TSC will not overflow within 10 years. This is far beyond a system’s uninterrupted operating time, therefore I see no reason for an overflow interrupt etc.
>> The common approach is to read and store the TSC at a tracepoint and calculate time differences between associated tracepoints. The main difficulty is to determine the absolute timebase, because this is highly dependent on the specific CPU and chipset in use, and on the system’s clocking.
>> TSCs count CPU core clock cycles. So it becomes somewhat iffy when you start frequency scaling. On some XScale processors you have the option of saving power by gating the core clock. IIRC that means also the TSC will be halted.
>> Unless you do the energy saving thing, it becomes pretty trivial to find out the core CPU frequency.
>> Under Linux 
>> cat /proc/cpuinfo
>> will tell you  and BIOS usually also does.
>> On Windows you can look up the System info.
>> 
>> Regards,
>>     Stefan.
>> --
>> Stefan M. Petters
>> CISTER Research Unit
>>  
>> ISEP - IPP | Rua Dr. António Bernardino de Almeida 431
>> 4200-072 Porto | Portugal 
>> T +351 22 83 40 529 | Homepage
> 
> 
> -- 
> Stefan M. Petters
> CISTER Research Unit
>  
> ISEP - IPP | Rua Dr. António Bernardino de Almeida 431
> 4200-072 Porto | Portugal 
> T +351 22 83 40 529 | Homepage
> _______________________________________________
> Developer mailing list
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