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    SubjectRe: [RFC/RFT PATCH v3] sched: automated per tty task groups
    On 2010.11.11 at 08:26 -0700, Mike Galbraith wrote:
    > I _finally_ got back to this yesterday, and implemented your suggestion,
    > though with a couple minor variations. Putting the autogroup pointer in
    > the signal struct didn't look right to me, so I plugged it into the task
    > struct instead. I also didn't refcount taskgroups, wanted the patchlet
    > to be as self-contained as possible, so refcounted the autogroup struct
    > instead. I also left group movement on tty disassociation in place, but
    > may nuke it.
    ...
    >
    > With taskset -c 3 make -j 10 running..
    >
    > taskset -c 3 ./wakeup-latency& sleep 30;killall wakeup-latency
    >
    > without:
    > maximum latency: 42963.2 µs
    > average latency: 9077.0 µs
    > missed timer events: 0
    >
    > with:
    > maximum latency: 4160.7 µs
    > average latency: 149.4 µs
    > missed timer events: 0

    Just to add some data; here are the results from my machine (AMD 4
    cores) running a -j4 kernel build, while I browsed the web:

    1) perf sched record sleep 30

    without:
    total_wakeups: 44306
    avg_wakeup_latency (ns): 36784
    min_wakeup_latency (ns): 0
    max_wakeup_latency (ns): 9378852

    with:
    total_wakeups: 43836
    avg_wakeup_latency (ns): 67607
    min_wakeup_latency (ns): 0
    max_wakeup_latency (ns): 8983036

    2) perf record -a -e sched:sched_switch -e sched:sched_wakeup sleep 10

    without:
    total_wakeups: 13195
    avg_wakeup_latency (ns): 48484
    min_wakeup_latency (ns): 0
    max_wakeup_latency (ns): 8722497

    with:
    total_wakeups: 14106
    avg_wakeup_latency (ns): 92532
    min_wakeup_latency (ns): 20
    max_wakeup_latency (ns): 5642393

    So the avg_wakeup_latency nearly doubled with your patch, while the
    max_wakeup_latency is lowered by a good amount.

    --
    Markus
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