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    SubjectRe: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

    On Tue, 20 Jan 2009, Ingo Molnar wrote:

    >
    > * Steven Rostedt <rostedt@goodmis.org> wrote:
    >
    > > On Tue, 20 Jan 2009, Ingo Molnar wrote:
    > > > Another test would be to build the scheduler latency tracer into your
    > > > kernel:
    > > >
    > > > CONFIG_SCHED_TRACER=y
    > > >
    > > > And enable it via:
    > > >
    > > > echo wakeup > /debug/tracing/current_tracer
    > > >
    > > > and you should be seeing the worst-case scheduling latency traces in
    > > > /debug/tracing/trace, and the largest observed latency will be in
    > > > /debug/tracing/tracing_max_latency [in microseconds].
    > >
    > > Note, the wakeup latency only tests realtime threads, since other
    > > threads can have other issues for wakeup. I could change the wakeup
    > > tracer as wakeup_rt, and make a new "wakeup" that tests all threads, but
    > > it may be difficult to get something accurate.
    >
    > hm, that's a significant regression then. The latency tracer used to
    > measure the highest-prio task in the system - be that RT or non-rt.

    Well, it is a regression from what was in -rt yes. But not from what ever
    was in mainline.

    But I needed to change this to detect the problem that we
    solved with push and pull of rt tasks. The wake up of a non-rt tasks
    always took longer than an -rt task, and by tracing all tasks, I never got
    the wake up latency of an rt task.

    As I mentioned earlier, I can make a wakeup-rt to do the rt tracing, and
    make wakeup do all tasks.

    -- Steve



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