lkml.org 
[lkml]   [2005]   [Jul]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: Realtime Preemption, 2.6.12, Beginners Guide?
    Date
    On Wednesday 06 Jul 2005 18:01, Ingo Molnar wrote:
    > * Alistair John Strachan <s0348365@sms.ed.ac.uk> wrote:
    > > > I'm beginning to understand the issue, and I see why you think the
    > > > proposed patch fixes it. I'll compile and boot V0.7.51-05 now.
    > >
    > > Indeed, this seems to have fixed it.
    > >
    > > ( softirq-timer/0-3 |#0): new 8 us maximum-latency wakeup.
    > > ( softirq-timer/0-3 |#0): new 9 us maximum-latency wakeup.
    > > ( softirq-timer/0-3 |#0): new 9 us maximum-latency wakeup.
    > > ( softirq-timer/0-3 |#0): new 9 us maximum-latency wakeup.
    > > ( softirq-timer/0-3 |#0): new 10 us maximum-latency wakeup.
    > > ( softirq-timer/0-3 |#0): new 14 us maximum-latency wakeup.
    >
    > great! Do the softlockup warnings still occur?

    Yes, but in no greater a number.

    [root] 18:09 [~] uptime
    18:09:39 up 19 min, 4 users, load average: 0.36, 0.29, 0.16

    [root] 18:09 [~] dmesg | grep BUG: | wc -l
    5

    So far, however, there have been no lockups! The previous kernels would die
    very obviously within a couple of minutes.

    I wonder if the ACPI problem was causing lockups (one thought I had was that
    the "ondemand" cpufreq governor was generating more ACPI events than usual,
    as the BIOS stepped through the different CPU speeds).

    >
    > > Find attached another trace (only 33us this time).
    >
    > the main latency comes from here:
    > > <...>-3485 0Dnh2 13us : enqueue_task (__schedule)
    > > <...>-3485 0Dnh2 14us+: trace_array (__schedule)
    > > <...>-3485 0Dnh2 18us : trace_array <softirq--3> (69 6e)
    > > <...>-3485 0Dnh2 18us : trace_array <<...>-3485> (76 78)
    > > <...>-3485 0Dnh2 20us+: trace_array (__schedule)
    > > softirq--3 0Dnh2 28us+: __switch_to (__schedule)
    >
    > trace_array() can be quite expensive (it generates a trace entry of
    > every runnable task, with interrupts and preemption disabled). It is
    > disabled if RT_DEADLOCK_DETECT is disabled. For pure wakeup latency
    > tracing, the most optimal combination of options is:
    >
    [snip]
    >
    > such a kernel will still be able to generate /proc/latency_trace traces,
    > but has much lower runtime overhead than your current kernel. (But you
    > should probably keep all debugging enabled until all of the current
    > problems have been resolved.)
    >
    > Ingo

    Well, thanks for the info. As you said, when the remaining issues have been
    resolved, I'll need to step up to a more efficient kernel, because I require
    extremely low kernel latency for the software I'm writing (this was not an
    idle patch fest).

    --
    Cheers,
    Alistair.

    personal: alistair()devzero!co!uk
    university: s0348365()sms!ed!ac!uk
    student: CS/CSim Undergraduate
    contact: 1F2 55 South Clerk Street,
    Edinburgh. EH8 9PP.
    -
    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: 2005-07-07 02:50    [W:5.376 / U:0.884 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site