>From a1aa992fb25fb8e98a5c5724376ae8cc91463de3 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
Date: Mon, 25 Jan 2016 23:05:36 -0500
Subject: [PATCH 2/2] powerpc/perf/hv-24x7: Display change in counter values
For 24x7 counters, perf displays the raw value of the 24x7 counter, which
is a monotonically increasing value.
perf stat -C 0 -e \
'hv_24x7/HPM_0THRD_NON_IDLE_CCYC__PHYS_CORE,core=1/' \
sleep 1
Performance counter stats for 'CPU(s) 0':
9,105,403,170 hv_24x7/HPM_0THRD_NON_IDLE_CCYC__PHYS_CORE,core=1/
0.000425751 seconds time elapsed
In the typical usage of 'perf stat' this counter value is not as useful
as the _change_ in the counter value over the duration of the application.
Have h_24x7_event_init() set the event's prev_count to the raw value of
the 24x7 counter at the time of initialization. When the application
terminates, hv_24x7_event_read() will compute the change in value and
report to the perf tool. Similarly, for the transaction interface, clear
the event count to 0 at the beginning of the transaction.
perf stat -C 0 -e \
'hv_24x7/HPM_0THRD_NON_IDLE_CCYC__PHYS_CORE,core=1/' \
sleep 1
Performance counter stats for 'CPU(s) 0':
245,758 hv_24x7/HPM_0THRD_NON_IDLE_CCYC__PHYS_CORE,core=1/
1.006366383 seconds time elapsed
Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
---
arch/powerpc/perf/hv-24x7.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index b7a9a03..77b958f 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c
@@ -1222,11 +1222,12 @@ static int h_24x7_event_init(struct perf_event *event)
return -EACCES;
}
- /* see if the event complains */
+ /* Get the initial value of the counter for this event */
if (single_24x7_request(event, &ct)) {
pr_devel("test hcall failed\n");
return -EIO;
}
+ (void)local64_xchg(&event->hw.prev_count, ct);
return 0;
}
@@ -1289,6 +1290,16 @@ 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);
--
2.5.3
