Linaro Multimedia WG project

hw perfevents on the pandabaord

Bug #744458 reported by Ken Werner on 2011-03-28

This bug affects 1 person

Affects		Status	Importance	Assigned to	Milestone
	Linaro Multimedia WG project	New	Low	Unassigned	Linaro Multimedia WG project 2011.09
	linux-linaro-omap (Ubuntu)	New	Undecided	Unassigned

Bug Description

The 2.6.38-1001-linaro-omap kernel reports "unable to reserve pmu" when attempting to access hw counters using perf:
<snip>
$ uname -a
Linux panda 2.6.38-1001-linaro-omap #2-Ubuntu SMP Mon Mar 21 21:40:07 UTC 2011 armv7l armv7l armv7l GNU/Linux

$ sudo su -c "echo -1 > /proc/sys/kernel/perf_event_paranoid" && cat /proc/sys/kernel/perf_event_paranoid
-1

  $ sudo ./perf stat -e r63 -- sleep 1
  No permission to collect stats.
  Consider tweaking /proc/sys/kernel/perf_event_paranoid.

$ dmesg | tail -1
[10985.304809] hw perfevents: unable to reserve pmu

$ sudo su -c "strace -e trace=perf_event_open ./perf stat -e r63 -- sleep 1"
perf_event_open(0x1ed338, 0x114c, 0xffffffff, 0xffffffff, 0) = -1 ENODEV (No such device)
</snip>

The perf_event_open syscall returns ENODEV but the kernel config looks sane to me:
<snip>
  $ grep -i perf_ /boot/config-2.6.38-1001-linaro-omap
  # CONFIG_DEBUG_PERF_USE_VMALLOC is not set
  CONFIG_HAVE_PERF_EVENTS=y
  CONFIG_HW_PERF_EVENTS=y
  CONFIG_PERF_COUNTERS=y
  CONFIG_PERF_EVENTS=y
  CONFIG_PERF_USE_VMALLOC=y
</snip>