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    SubjectRe: [PATCH 0/4] perf: Precise task / softirq / hardirq filtered stats/profiles

    * Frederic Weisbecker <> wrote:

    > Hi,
    > The new task and irq exclusion handling can let you
    > confine tracing and profiling to about everything you
    > want.

    I fixed the subject line ;-)

    'exclusion' is the ABI detail. The feature your patches
    implement are to allow 'softirq limited' or 'task-context
    limited' or 'hardirq profiling' - which is way cool.

    One thing i'd like to see in this feature is for it to
    work on pure event counting - i.e. 'perf stat' as well.

    This would allow some _very_ precise stats, without IRQ
    noise. For example, today we have this kind of noise
    in instruction counting:

    $ for ((i=0;i<10;i++)); do perf stat -e instructions /bin/true 2>&1 | grep instructions; done
    217161 instructions # 0,000 IPC
    218591 instructions # 0,000 IPC
    223268 instructions # 0,000 IPC
    217112 instructions # 0,000 IPC
    219392 instructions # 0,000 IPC
    216801 instructions # 0,000 IPC
    217501 instructions # 0,000 IPC
    218565 instructions # 0,000 IPC
    218682 instructions # 0,000 IPC
    218523 instructions # 0,000 IPC

    it it's all that bad at ~2% jitter, but many improvements
    we are working on in the kernel are much smaller than 1%.

    If we extended your feature to perf stat, we might be able
    to get a lot more precise measurements in terms of kernel
    optimizations (and kernel bloat).

    I'm really curious how accurate your scheme could become
    that way. From the above 'few thousands instructions'
    noise we might be able to get down to a 'hundreds of
    instructions' noise? If so then it would allow us to
    measure micro-optimizations in a radically more precise



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