The PERF_EVENT_IOC_PERIOD ioctl command can be used to change the
sample period of a running perf_event. Consequently, when calculating
the next event period, the new period will only be considered after the
previous one has overflowed.

This patch changes the calculation of the remaining event ticks so that
they are offset if the period has changed.

See commit 3581fe0e ("ARM: 7556/1: perf: fix updated event period in
response to PERF_EVENT_IOC_PERIOD") for details.
Signed-off-by: Young Xiao <92siuyang@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>