[LTP] [PATCH 2/2] syscalls/perf_event_open{01, 02}: Add -n arg for size of idle loop

[Cyril Hrubis]

Hi!
> The value of this option is used in do_word() idle loop. By default
> do_work() iterates 1000000000 times. However such loop may take a
> long time to finish for all available performance counters on some
> boards. It would be useful to have an ability to choose the size of
> idle loop.

Ideally LTP testcases should run just fine without any specific tweaks.

Looking at the code for perf_event_open01.c we can simply change the
predefined value of loops. Since this is just a basic test that enables
the interface and reads the values but does not try do anything with
them. The test would run just fine even if we didn't do anything in
between ENABLE and DISABLE ioctls().

The perf_event_open02.c is a bit more complicated, it test grouping and
multiplexing. Looking at the test it runs for about 4 second on a cheap
notebook so I can imagine that it takes couple of minutes on slow
hardware. I guess that we can safely divide the nunber of default loops
by 10 and everything should continue just fine.

So would diving by 10 work for you?


If that is still too slow we can always change the test to setup an
timer that would send a signal which would set set a variable which
would stop the loop in do_work() so that the test runs defined amount of
time regardless of the machine speed.

Or we could measure how long reasonably small number of iterations takes
in order to callibrate the number of loops the do_work() function should
do.

-- 
Cyril Hrubis
chrubis@suse.cz