repost attempt - kernel.org correctly rejects html email - i blame
gmail - hopefully fixed
On Fri, Sep 2, 2011 at 7:19 AM, Michael Mueller <ss7box@xxxxxxxxx> wrote:
>
>
> On Fri, Sep 2, 2011 at 3:37 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>>
>> Mike,
>>
>> On Thu, 1 Sep 2011, Michael Mueller wrote:
>> > On Thu, Sep 1, 2011 at 3:33 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> > wrote:
>> >
>> > >
>> > > That looks like a problem in the clocksource. i.e. time is going
>> > > backward or having weird momentary jumps. You could verify that by
>> > > running one ore more tight loops which do
>> > >
>> > > clock_gettime(CLOCK_MONOTONIC, &prev);
>> > > while (1) {
>> > > clock_gettime(CLOCK_MONOTONIC, &curr);
>> > > if (curr < prev) /* Use a proper compare function for
>> > > timespec! */
>> > > printf(.....);
>> > > prev = curr;
>> > > }
>> > >
>> > > If that triggers on RT or on a vanilla kernel, then the problem is
>> > > definitely somewhere in the timekeeping/clocksource area.
>> >
>> >
>> > have seen this problem in vanilla kernels; developed a work-around that
>> > calls
>> > clock_gettime(CLOCK_MONOTONIC, &curr); until curr>prev
>> > a couple of times, and if that doesn't work, then it gets a new prev
>> > value
>> > and a new curr value; rinse and repeat until curr<prev; not sure what
>> > precipitates the problem; will post workaround code if wanted
>>
>> Is that on a Panda board as well?
>
> older and newer Dell boxes with 2.6.old kernels; a few weeks ago I
> discovered a newer box time leaping/lagging so much that I had to throttle
> back the syslog messages indicating detection/correction
> if needed I can try to isolate and gather more info - see if a newer kernel
> generates the problem
> edit above: rinse and repeat until curr>prev
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