Re: [PATCH 48/52] tools/power: turbostat: fix large c1% issue

Konrad Rzeszutek Wilk
2012-07-25T13:12:11Z

On Tue, Jul 24, 2012 at 11:41:44PM -0400, Len Brown wrote:
> 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

calculated.

> 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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