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    SubjectRe: [PATCH 3/3] ftrace: function tracer with irqs disabled

    * Steven Rostedt <rostedt@goodmis.org> wrote:

    > > > > tracing type times entries recorded
    > > > > ------------ -------- ----------------
    > > > > irq disabled 43.393 166433066
    > > > > 43.282 166172618
    > > > > 43.298 166256704
    > > > >
    > > > > preempt disabled 38.969 159871710
    > > > > 38.943 159972935
    > > > > 39.325 161056510

    > When we used the preempt disabled version, we lost 5 million traces,
    > as suppose to the irq disabled which was only 1,150 traces lost.
    >
    > Considering that we had 166,256,704 traces total, that 5 million is
    > only 4% lost of traces. Still quite a lot. But again, this is an
    > extreme, because we are tracing hackbench.

    there's about 10% difference between the two hackbench results - so
    the lack of 5% of the traces could make up for about half of that
    overhead.

    anyway, that still leaves the other 5% as the _true_ overhead of IRQ
    disable.

    is there some other workload that does not lose this many trace
    entries, making it easier to compare irqs-off against preempt-off?

    Ingo


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