Re: [PATCH v7 1/5] powerpc/perf/hv-24x7: Fix inconsistent output values incase multiple hv-24x7 events run

Madhavan Srinivasan
2020-04-29T08:56:44Z

On 3/27/20 12:06 PM, Kajol Jain wrote:
> Commit 2b206ee6b0df ("powerpc/perf/hv-24x7: Display change in counter
> values")' added to print _change_ in the counter value rather then raw
> value for 24x7 counters. Incase of transactions, the event count
> is set to 0 at the beginning of the transaction. It also sets
> the event's prev_count to the raw value at the time of initialization.
> Because of setting event count to 0, we are seeing some weird behaviour,
> whenever we run multiple 24x7 events at a time.
>
> For example:
>
> command#: ./perf stat -e "{hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/,
> hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/}"
> -C 0 -I 1000 sleep 100
>
> 1.000121704 120 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 1.000121704 5 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 2.000357733 8 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 2.000357733 10 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 3.000495215 18,446,744,073,709,551,616 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 3.000495215 18,446,744,073,709,551,616 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 4.000641884 56 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 4.000641884 18,446,744,073,709,551,616 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 5.000791887 18,446,744,073,709,551,616 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
>
> Getting these large values in case we do -I.
>
> As we are setting event_count to 0, for interval case, overall event_count is not
> coming in incremental order. As we may can get new delta lesser then previous count.
> Because of which when we print intervals, we are getting negative value which create
> these large values.
>
> This patch removes part where we set event_count to 0 in function
> 'h_24x7_event_read'. There won't be much impact as we do set event->hw.prev_count
> to the raw value at the time of initialization to print change value.
>
> With this patch
> In power9 platform
>
> command#: ./perf stat -e "{hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/,
> hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/}"
> -C 0 -I 1000 sleep 100
>
> 1.000117685 93 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 1.000117685 1 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 2.000349331 98 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 2.000349331 2 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 3.000495900 131 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 3.000495900 4 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 4.000645920 204 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
> 4.000645920 61 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=1/
> 4.284169997 22 hv_24x7/PM_MCS01_128B_RD_DISP_PORT01,chip=0/
>
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
> Suggested-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>

Tested-by: Madhavan Srinivasan <maddy@linux.ibm.com>

> ---
> arch/powerpc/perf/hv-24x7.c | 10 ----------
> 1 file changed, 10 deletions(-)
>
> diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
> index 573e0b309c0c..48e8f4b17b91 100644
> --- a/arch/powerpc/perf/hv-24x7.c
> +++ b/arch/powerpc/perf/hv-24x7.c
> @@ -1400,16 +1400,6 @@ static void h_24x7_event_read(struct perf_event *event)
> h24x7hw = &get_cpu_var(hv_24x7_hw);
> h24x7hw->events[i] = event;
> put_cpu_var(h24x7hw);
> - /*
> - * Clear the event count so we can compute the _change_
> - * in the 24x7 raw counter value at the end of the txn.
> - *
> - * Note that we could alternatively read the 24x7 value
> - * now and save its value in event->hw.prev_count. But
> - * that would require issuing a hcall, which would then
> - * defeat the purpose of using the txn interface.
> - */
> - local64_set(&event->count, 0);
> }
>
> put_cpu_var(hv_24x7_reqb);