Commit 2b206ee6 authored Jan 25, 2016 by Sukadev Bhattiprolu Committed by Michael Ellerman Mar 10, 2016

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 <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent e5a5886d

arch/powerpc/perf/hv-24x7.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -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);

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