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    SubjectRe: change in sched cpu_power causing regressions with SCHED_MC
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    On Fri, 2010-02-19 at 10:36 -0800, Suresh Siddha wrote:
    > exec/fork balance is not broken. i.e., during exec/fork we balance the
    > load equally among sockets/cores etc. What is broken is:
    >
    > a) In SMT case, once we end up in a situation where both the threads of
    > the core are busy , with another core completely idle, load balance is
    > not moving one of the threads to the idle core. This unbalanced
    > situation can happen because of a previous wake-up decision and/or
    > threads on other core went to sleep/died etc. Once we end up in this
    > unbalanced situation, we continue in that state with out fixing it.
    >
    > b) Similar to "a", this is MC case where we end up four cores busy in
    > one socket with other 4 cores in another socket completely idle. And
    > this is the situation which we are trying to solve in this patch.
    >
    > In your above example, we test mostly fork/exec balance but not the
    > above sleep/wakeup scenarios.

    Ah, indeed. Let me extend my script to cover that.

    The below script does indeed show a change, but the result still isn't
    perfect, when I do ./show-loop 8, it starts 8 loops nicely spread over 2
    sockets, the difference is that all 4 remaining would stay on socket 0,
    the patched kernel gets 1 over to socket 1.


    ---

    NR=$1; shift

    cleanup()
    {
    killall loop
    }

    show_each_loop()
    {
    KILL=$1

    ps -deo pid,sgi_p,cmd | grep loop | grep bash | while read pid cpu cmd; do

    SOCKET=`cat /sys/devices/system/cpu/cpu${cpu}/topology/physical_package_id`
    CORE=`cat /sys/devices/system/cpu/cpu${cpu}/topology/core_id`
    SIBLINGS=`cat /sys/devices/system/cpu/cpu${cpu}/topology/thread_siblings_list`

    printf "loop-%05d on CPU: %02d SOCKET: %02d CORE: %02d THREADS: ${SIBLINGS} " $pid $cpu $SOCKET $CORE

    if [ $SOCKET -eq $KILL ]; then
    kill $pid;
    printf "(killed)"
    fi

    printf "\n"
    done
    }

    trap cleanup SIGINT

    echo "starting loops..."

    for ((i=0; i<NR; i++)) ; do
    ./loop &
    done

    sleep 1;

    echo "killing those on socket 1..."
    echo ""

    show_each_loop 1

    echo ""
    echo "watching load-balance work..."
    echo ""

    while sleep 1 ; do

    show_each_loop -1 | sort | awk '{socket[$6]++; th[$8 + (256*$6)]++; print $0}
    END { for (i in socket) { print "socket-" i ": " socket[i]; }
    for (i in th) { if (th[i] > 1) { print "thread-" int(i/256)"/"(i%256) ": " th[i]; } } }'

    echo ""
    echo "-------------------"
    echo ""

    done





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