opreport appears to not support changing events

Original mailing list thread:
http://marc.info/?l=oprofile-list&m=128508347501923&w=2

If a user starts a profile run with one set of counters, and then changes the counters they want to profile without shutting down the daemon, opreport reports on the old counters. Here is a sample session demonstrating the confusion:

[reid@muikyl profiling]$ sudo opcontrol --reset && sudo opcontrol
--start -e CPU_CLK_UNHALTED:400000 -e INST_RETIRED:400000 &&
./matrix_multiply && sudo opcontrol --stop
Signalling daemon... done
Profiler running.
Setup
Running matrix_multiply_run()...
Elapsed execution time: 11.496006 sec
Stopping profiling.
[reid@muikyl profiling]$ opreport ./matrix_multiply
Overflow stats not available
CPU: Intel Core/i7, speed 1596 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a
unit mask of 0x00 (No unit mask) count 1000000
Counted INST_RETIRED events (number of instructions retired) with a
unit mask of 0x01 (any_p instructions retired) count 1000000
CPU_CLK_UNHALT...|INST_RETIRED:1...|
samples| %| samples| %|
------------------------------------
22925 100.000 9056 100.000 matrix_multiply
[reid@muikyl profiling]$ sudo opcontrol --reset && sudo opcontrol
--start -e L1D:400000 -e MEM_INST_RETIRED:400000 && ./matrix_multiply
&& sudo opcontrol --stop
Signalling daemon... done
Profiler running.
Setup
Running matrix_multiply_run()...
Elapsed execution time: 11.494934 sec
Stopping profiling.
[reid@muikyl profiling]$ opreport ./matrix_multiplyOverflow stats not available
CPU: Intel Core/i7, speed 1596 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a
unit mask of 0x00 (No unit mask) count 1000000
Counted INST_RETIRED events (number of instructions retired) with a
unit mask of 0x01 (any_p instructions retired) count 1000000
CPU_CLK_UNHALT...|INST_RETIRED:1...|
samples| %| samples| %|
------------------------------------
22919 100.000 9056 100.000 matrix_multiply

opcontrol --status reports that the new counters are being used, even though they didn't show up in the report:

[reid@muikyl profiling]$ sudo opcontrol --status
Daemon running: pid 2341
Event 0: L1D:400000:1:1:1
Event 1: MEM_INST_RETIRED:400000:1:1:1
Separate options: none
vmlinux file: none
Image filter: none
Call-graph depth: 0

Maynard suggested that the solution might be to keep a second cache of the set of performance counters being monitored, but I am not familiar enough to explain more.