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    SubjectRe: [RFC] [rt-tests] change to cyclictest behavior
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    On Wed, Jan 6, 2010 at 8:04 PM, Clark Williams <williams@redhat.com> wrote:
    > RT-ers,
    >
    > I have a problem with the way cyclictest sets up measurement threads,
    > but before I went and changed things I thought I would ask if people
    > cherished this particular behavior.
    >
    > Currently, when cyclictest is run with multiple threads (i.e. -t
    > option) it distributes both the sample interval and the realtime
    > priority by adding the 'distance' parameter to the interval and
    > decrementing the priority by one. This means if you have a distance of
    > 500us (default), a specified RT priority of 95 and start four threads,
    > they will be started with the following parameters:
    >
    > $ cyclictest -t4 -p95
    >
    > Will give you:
    >
    > thread          priority        sample interval
    > 0               95              500
    > 1               94              1000
    > 2               93              1500
    > 3               92              2000
    >
    > What I'd like to do is modify this logic so that when '-a' (affinity) is
    > specified, the priority and sample interval will not be altered. I
    > don't think there's any point in distributing the priority's and
    > sample intervals when the measurement threads are pinned to their own
    > CPU.
    >
    > So:
    >
    > $ cyclictest -t4 -p95 -a
    >
    > Would have each thread at SCHED_FIFO 95 and a sample interval of 500us.
    >
    > Note that this behavior also occurs when the histogram (-h) option is
    > specified).
    >
    > Thoughts?
    >

    Seems reasonable to me. Maybe it would also be nice to have a flag to
    get the old behaviour back even with -a?

    John
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