pstop uses several keys. Help is available by pressing 'h'. This is what
it tells you.

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pstop version 0.0.10 (C) 2014 Simon J Mudd <sjmudd@pobox.com>

Program to show the top I/O information by accessing information from the
performance_schema schema. Ideas based on mysql-sys.

Keys:
- - reduce the poll interval by 1 second (minimum 1 second)
+ - increase the poll interval by 1 second
h - this help screen
q - quit
t - toggle between showing time since resetting statistics or since P_S data was collected
z - reset statistics
<tab> - change display modes between: latency, ops, file I/O and lock modes