lkml.org 
[lkml]   [2006]   [Feb]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [BUG -rt] -rt16 hang w/ realtime thread test
    From
    Date
    On Sat, 2006-02-11 at 10:34 -0500, Steven Rostedt wrote:
    > On Fri, 10 Feb 2006, john stultz wrote:
    >
    > > Hey Ingo,
    > > I've been hunting a report that lower priority realtime threads are not
    > > preempting higher priority realtime threads. However, in generating test
    > > cases, I found I was locking the system quite frequently.
    > >
    > > The attached test runs to completion on 2.6.15, but with 2.6.15-rt16, it
    > > hangs the box. It could very well be a test issue, but I'm not sure I
    > > see where the problem is.
    > >
    >
    > Hi John,
    >
    > Have you turned on nmi_watchdog and softlockup detect? Just so we can see
    > where it is hung.

    Ugh. Ok, I think I've found the issue.

    The systems I'm testing w/ all use the ACPI PM timer for the
    clocksource. On a whim I forced the TSC to be used and the hang went
    away.

    It appears the issue is that the ACPI PM wraps every ~5 seconds. Since
    the test takes longer the 5 seconds to run, the
    timeofday_periodic_hook() function gets starved and we never accumulate
    time. Then as the counter wraps, time starts wrapping thus timers do not
    expire and the test never completes, effectively hanging the box.

    I believe this issue was hit before back when cycle_t was 32bits long,
    thus causing the TSC to wrap every ~4seconds on a 1Ghz box.

    So whats the solution here? Do we need to do something to
    timeofday_periodic_hook is guaranteed to run with some frequency? Or is
    the test just bunk because realtime threads must give up the cpu in
    order for the kernel to function?

    Thoughts?
    -john



    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-02-14 02:56    [W:0.032 / U:0.208 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site