cyclictest: add align thread wakeup times option
This patch provides and additional -A/--align flag to cyclictest to align
thread wakeup times of all threads as closly defined as possible.
When running multiple threads in cyclictest (-S or -t # option) the threads
are launched in an unsynchronized manner. Basically the creation order and
time for thread creation determines the start time. For provoking a maximum
congestion situation (e.g. cache evictions) and to improve reproducibility
or run conditions the start time should be defined distances appart. The
well defined distance is implemented as a offset parameter to -A/--align
and will offset each threads start time by the parameter * the sequentially
assigned thread number (par->tnum), together with the -d0 (distance in the
intervals of the individual threads) this alignment option allows to get
the thread wakeup times as closely synchronized as possible.
The method to sync is simply that the thread with par->tnum == 0 is chosen
to set a globally shared timestamp, and all other threads use this timestamp
as their starting time rather than each calling clock_gettime() at startup.
To ensure synchronization of the thread startup the setting of the global
time is guarded by pthread_barriers.
Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Reviewed-by: Andreas Platschek <andreas.platschek@opentech.at>
Signed-off-by: Clark Williams <clark.williams@gmail.com>
2 files changed
