Re: Computing cpu's clock in cycles per second

[Wade Hampton]

Did you look at using the RDTSC instruction to read the
cycle counter?

http://en.wikipedia.org/wiki/Time_Stamp_Counter

Sample this over an interval to get an estimate
of the clock frequency based on this counter.

__inline__ unsigned long long int rdtsc()
{
  unsigned long long int x;
  __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
  return(x);
}

I use gettimeofday() calls to check the wall-clock time,
usleep(n) to sleep for a long time (second or more),
and rdtsc to compute the cycles....  Seems to work
well.

Cheers,
--
Wade Hampton

Computing cpu's clock in cycles per second

[JD]

On 09/27/2010 07:34 AM, Wade Hampton wrote:
> Did you look at using the RDTSC instruction to read the
> cycle counter?
>
> http://en.wikipedia.org/wiki/Time_Stamp_Counter
>
> Sample this over an interval to get an estimate
> of the clock frequency based on this counter.
>
> __inline__ unsigned long long int rdtsc()
> {
>    unsigned long long int x;
>    __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
>    return(x);
> }
>
> I use gettimeofday() calls to check the wall-clock time,
> usleep(n) to sleep for a long time (second or more),
> and rdtsc to compute the cycles....  Seems to work
> well.
> Cheers,
>
> Wade Hampton

Thank you very much Wade.
I confirm that using rdtsc, the delta in tsc values, divided by 60 
(using nanosleep)
is  798283074.9833333333 ticks per second, which is almost iddentical
to what is reported by cpuinfo:
cpu MHz        : 798.244

No matter what the load factor on the machine, even when the load 
reached 5 or  6,
it is the same value.
Well, that's what you get for buying a laptop from a crappy manufacturer
that has put in it a fixed unprogrammable clock (oscillator), and put in a
lame BIOS that provides no hooks for setting C2 C3 ...etc.
I will certainly steer friends and family away from this manufacturer.

Computing cpu's clock in cycles per second

[Michael Miles]

JD wrote:
> On 09/27/2010 07:34 AM, Wade Hampton wrote:
> > Did you look at using the RDTSC instruction to read the
> > cycle counter?
> >
> > http://en.wikipedia.org/wiki/Time_Stamp_Counter
> >
> > Sample this over an interval to get an estimate
> > of the clock frequency based on this counter.
> >
> > __inline__ unsigned long long int rdtsc()
> > {
> >     unsigned long long int x;
> >     __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
> >     return(x);
> > }
> >
> > I use gettimeofday() calls to check the wall-clock time,
> > usleep(n) to sleep for a long time (second or more),
> > and rdtsc to compute the cycles....  Seems to work
> > well.
> > Cheers,
> >
> > Wade Hampton
>
> Thank you very much Wade.
> I confirm that using rdtsc, the delta in tsc values, divided by 60
> (using nanosleep)
> is  798283074.9833333333 ticks per second, which is almost iddentical
> to what is reported by cpuinfo:
> cpu MHz        : 798.244
>
> No matter what the load factor on the machine, even when the load
> reached 5 or  6,
> it is the same value.
> Well, that's what you get for buying a laptop from a crappy manufacturer
> that has put in it a fixed unprogrammable clock (oscillator), and put in a
> lame BIOS that provides no hooks for setting C2 C3 ...etc.
> I will certainly steer friends and family away from this manufacturer.

I find the whole idea of a manufacturer purposely sabotaging a computer 
in this manner just disgraceful.

This one really takes the cake since "cool and quiet" and "powernow" was 
a big marketing scheme back then. You would think that the bios would at 
least have something to say about it

I wonder if the machine in question was on windows if the cool and quiet 
drivers would have something to enable/ disable them by software?
But then again if Bios does not support then that would be a no show too...

Very bad manufacturing screw up

Michael