missing perf events from some cpu(s)

[graphaelli]

While working on #124, not as many events came through as expected. It turns out that events from the second cpu (of 2) were not coming through at all. I verified this by pinning the producer process to each cpu with taskset and confirming that events only appeared with taskset -c 0 and not taskset -c 1

$ cat /sys/devices/system/cpu/online
0-1

In contrast, with bcc (trace.py) all events come through regardless of taskset.