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    Subject[PATCH 48/52] tools/power: turbostat: fix large c1% issue
    Date
    From: Len Brown <len.brown@intel.com>

    Under some conditions, c1% was displayed as very large number,
    much higher than 100%.

    c1% is not measured, it is derived as "that, which is left over"
    from other counters. However, the other counters are not collected
    atomically, and so it is possible for c1% to be calaculagted as
    a small negative number -- displayed as very large positive.

    There was a check for mperf vs tsc for this already,
    but it needed to also include the other counters
    that are used to calculate c1.

    Signed-off-by: Len Brown <len.brown@intel.com>
    ---
    tools/power/x86/turbostat/turbostat.c | 12 ++++++++----
    1 file changed, 8 insertions(+), 4 deletions(-)

    diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
    index b815a12..861d771 100644
    --- a/tools/power/x86/turbostat/turbostat.c
    +++ b/tools/power/x86/turbostat/turbostat.c
    @@ -444,6 +444,9 @@ delta_core(struct core_data *new, struct core_data *old)
    old->c7 = new->c7 - old->c7;
    }

    +/*
    + * old = new - old
    + */
    void
    delta_thread(struct thread_data *new, struct thread_data *old,
    struct core_data *core_delta)
    @@ -482,19 +485,20 @@ delta_thread(struct thread_data *new, struct thread_data *old,


    /*
    - * As mperf and tsc collection are not atomic,
    - * it is possible for mperf's non-halted cycles
    + * As counter collection is not atomic,
    + * it is possible for mperf's non-halted cycles + idle states
    * to exceed TSC's all cycles: show c1 = 0% in that case.
    */
    - if (old->mperf > old->tsc)
    + if ((old->mperf + core_delta->c3 + core_delta->c6 + core_delta->c7) > old->tsc)
    old->c1 = 0;
    else {
    /* normal case, derive c1 */
    old->c1 = old->tsc - old->mperf - core_delta->c3
    - core_delta->c6 - core_delta->c7;
    }
    +
    if (old->mperf == 0) {
    - if (verbose) fprintf(stderr, "cpu%d MPERF 0!\n", old->cpu_id);
    + if (verbose > 1) fprintf(stderr, "cpu%d MPERF 0!\n", old->cpu_id);
    old->mperf = 1; /* divide by 0 protection */
    }

    --
    1.7.12.rc0


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