Experimental Physics and
Industrial Control System

Andy Foster <[email protected]> · Thu, 26 Apr 2001 12:26:03 +0000

Dear All,

Has anyone experienced a task crash caused by the "devVXStats" support
in 3.13.4?

I have just added the database records for this. I'm running on
an MVME2700 PPC. The system is apparently about 7% loaded according
to the report from the device support. I'm sampling the CPU load every
5 seconds, although I have varied this with the same outcome.

I traced the crash to line 373 of "devVXStats.c" (in the function "getCpu"):

temp = 100.0 * temp/ticksNow;

It appears to be possible for "ticksNow" to be 0 at this point.

I added a conditional check on "pcpuUsage->ticksNow" so that the code
only gets executed if this value is non-zero (adding a printf statement so
that I could see how many crashes I would have had):

static double getCpu()
{
    if((pcpuUsage->didNotComplete && pcpuUsage->nBurnNow==0) || !pcpuUsage->ticksNow) {
        if( !pcpuUsage->ticksNow )
          printf("This would have been a crash\n");
        pcpuUsage->usage = 0.0;
    } else {
        double temp;
        double ticksNow,nBurnNow;

        ticksNow = (double)pcpuUsage->ticksNow;
        nBurnNow = (double)pcpuUsage->nBurnNow;
        ticksNow *= (double)pcpuUsage->nBurnNoContention/nBurnNow;
        temp = ticksNow - (double)pcpuUsage->ticksNoContention;
        temp = 100.0 * temp/ticksNow;
        if(temp<0.0 || temp>100.0) temp=0.0;/*take care of tick overflow*/
        pcpuUsage->usage = temp;
    }
    pcpuUsage->didNotComplete = TRUE;
    semGive(pcpuUsage->startSem);
    return(pcpuUsage->usage);
}

I saw the statement about 4 times in 1 hour on the console.
I'm not sure why "pcpuUsage->ticksNow" is zero, but I think it might be
worth adding in the check just to be defensive.

Cheers,

Andy

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System