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Subject: Kernel 2.6.27.7-9 for Suse 11.1 help required with CPU Clock freq/speed/ticks
Date: Fri, 20 Nov 2009 10:57:47 -0000
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Thread-Topic: Kernel 2.6.27.7-9 for Suse 11.1 help required with CPU Clock freq/speed/ticks
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From: "Ahmed, Subhan (UK)" <Subhan.Ahmed@baesystems.com>
To: <linux-kernel@vger.kernel.org>
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Hi All,

I know this is not email list for programming questions but it relates
to Kernel as well, in fact relying on kernel. Could someone please
through a light or guide me to the right direction.


Problem Statement:	High CPU clock speed/freq
Requirement:		Obtain a stable CPU clock ticks/speed/freq on
Suse 11.1 with kernel 2.6.27.7-9
Questions:			Please refer to the bottom of this page
Artifacts in Use:
-----------------------------------
OS:					Suse 11.1
GCC Version:		4.3.2 (Suse Linux) [gcc_4_3-brach revision
141291]
Kernel:				2.6.27.7-9
Kernel Mods:		
					* Un-check the Tickless option
					* Timer Frequency - 1000Hz
					* Preempt kernel

Others 1
-----------
OS:					Suse 10.2
GCC Version:		4.1.2 20061115 (prerelease)(SUSE Linux)
Kernel:				2.6.18.2-34-default
Kernel Mods:
					* Preemptible Kernel
(Low-Latency Desktop) (NEW)
					* Preempt The Big Kernel Lock
(NEW)
					* Timer frequency (NEW) - 1000
Hz (NEW)

Others 2
-----------
OS:					Suse 9.3
GCC Version:		3.3.5 20050117 (prerelease)(SUSE Linux)
Kernel				2.6.11.4-20a-default
Kernel Mods:		None

I executed the following c++ code on the above stated builds

CODE - file name test.cpp
#include <signal.h>
#include <sys/time.h>
#include <iostream>
#include <cstdlib>


using namespace std;

long long int counter = 0;
struct timeval last_time;
struct timeval curr_time;
double dif = 0.0;
double freq_sum = 0.0;
double reps = 0.0;
double freq_min = 99999.0;
double freq_max = 0.0;
long long int num_too_low = 0;

void time_check(int data)
{
    // work out the frequecy of the SIGALRMs
    ++counter;
    if (counter >= 1000)
    {

        // need to work out time since last 1000 ticks
	gettimeofday(&curr_time, NULL);
	dif = ((curr_time.tv_usec + curr_time.tv_sec * 1000000)
		- (last_time.tv_usec + last_time.tv_sec * 1000000));
        double freq = (counter / dif)  * 1000000;

        freq_sum = ((freq_sum * reps) + freq) / (reps + 1) ;

        ++reps;
        cout << "Frequency = " << freq << " reps= " << dif / 1000000 <<
endl;
        if (freq_min > freq) freq_min = freq;
        if (freq_max < freq) freq_max = freq;
        if (freq < 950) 
            ++num_too_low;
        last_time = curr_time;
        counter = 0;
    }
}

int main (int argc, char * argv[])
{
    cout << "go" /* << "\a \a \a" */ << endl;
	
    int res;
    gettimeofday(&last_time, NULL);
    struct sigaction action;

    struct itimerval timer_value;

    timer_value.it_value.tv_sec = 0;
    timer_value.it_value.tv_usec = 1;
    timer_value.it_interval.tv_sec = 0;
    timer_value.it_interval.tv_usec = 1;

    action.sa_handler = time_check;
    action.sa_flags = SA_NOMASK;
    sigemptyset(&action.sa_mask);

    sigaction( SIGALRM, &action, NULL);
    res = setitimer( ITIMER_REAL, &timer_value, NULL );
    if (res == -1)
        cout << "error in setitimer" << endl;

    cout << "Starting CPU Test program" << endl;
    // loop for a long time

    while (reps < 3000.0)
    {
        sleep(1);
    }
    cout << "average CPU frequency = " << freq_sum << endl;
    cout << "reps = " << reps << endl;
    cout << "Min = " << freq_min << "  Max = " << freq_max << endl;
    cout << "number of low = " << num_too_low << endl;
    return 0;
}

Compiled the above code with 	"g++ -o test test.cpp"
Run the above code with 		"./test"

Observations:
SUSE Version    AVG. Frequency        		AVG. REPS
Suse 9.3  		999.xxx to 990.xxx  			reps > 1
(on average)
Suse 10.2 		999.xxx to 998.xxx  			reps (1
- 1.001)
Suse 10.3     	1000.xxx to 912.xxx  			reps (1 - 1.090)
Suse 11.1       0 to  324263.xxx  				reps
(-2e-0.6 upto 0.005112)

Suse 11.1 - Options:

- Turn off ACPI in options when booting with clock=tsc | clock=pit

Observations for suse 11.1 with options acpi=off and clock=tsc |
clock=pit

SUSE Version    AVG. Frequency        		AVG. REPS
Suse 11.1 		710.xxx to 999.xxx      		reps
(1.37xx to 1.0002)

Hardware used for Suse 11.1 - HP Pavilion Slimline s3821uk Desktop PC
(NQ808AA) specifications - HP Home & Home Office products
http://h10010.www1.hp.com/wwpc/uk/en/ho/WF10a/12454-12454-3329740-64546-
64546-3884669.html?jumpid=in_r2515_uk/en/hho/ipg/psc404redirect-ot-xx-xx
-/chev/

While testing no other application/s were running.

Question:

* Is my c++ code correct?
* Am I using the correct way to get the clock ticks or is there more
reliable tchnique avaliable to do this?
* Is that a problem with new Kernel if so is it a known issue ?
* Do I need to modify the Kernel to obtain regular and stable clock tick
at 1000 Hz ?
* Do I have to upgrade the Kernel ?
* Would be great, if pointed to the right direction for solution (e.g.
another forum) if no solution at hand.

Thanks

Subhan

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