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    SubjectRe: [accounting regression since rc1] scheduler updates

    * Christian Borntraeger <borntraeger@de.ibm.com> wrote:

    > Am Montag, 20. August 2007 schrieb Ingo Molnar:
    > > could you send that precise sched_clock() patch? It should be an order
    > > of magnitude simpler than the high-precision stime/utime tracking you
    > > already do, and it's needed for quality scheduling anyway.
    >
    > I have a question about that. I just played with sched_clock, and even
    > when I intentionally slow down sched_clock by a factor of 2, my cpu
    > bound process gets 100 % in top. If this is intentional, I dont
    > understand how a virtualized sched_clock would fix the accounting
    > change?

    could you try the patch below, does it work any better?

    Ingo

    ---
    kernel/sched.c | 9 +++++++++
    1 file changed, 9 insertions(+)

    Index: linux/kernel/sched.c
    ===================================================================
    --- linux.orig/kernel/sched.c
    +++ linux/kernel/sched.c
    @@ -333,6 +333,14 @@ static void __update_rq_clock(struct rq
    #ifdef CONFIG_SCHED_DEBUG
    WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
    #endif
    +#ifdef CONFIG_VIRT_CPU_ACCOUNTING
    + /*
    + * Trust sched_clock on s390:
    + */
    + if (unlikely(delta > rq->clock_max_delta))
    + rq->clock_max_delta = delta;
    + clock += delta;
    +#else
    /*
    * Protect against sched_clock() occasionally going backwards:
    */
    @@ -355,6 +363,7 @@ static void __update_rq_clock(struct rq
    clock += delta;
    }
    }
    +#endif

    rq->prev_clock_raw = now;
    rq->clock = clock;
    -
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