Authors: Joerg Behrens; Hendryk Bockelmann

Copyright: Copyright (C) 2017 Joerg Behrens behre.nosp@m.ns@d.nosp@m.krz.d.nosp@m.e, Hendryk Bockelmann bocke.nosp@m.lman.nosp@m.n@dkr.nosp@m.z.de

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The basic idea

The SCT library was invented with the aim of having an easy to use timer with as little overhead as possible. The timers (which can also measure hardware performance counters via PAPI interface) are implemented for pure sequential, OpenMP, MPI and hybrid OpenMP-MPI usage with a special emphasis on selectable reduction operations in order to provide a compact presentation of the measurments of parallel applications.

Examples

All timer usage should be initializes by the call

timer_size = sct_init(timer_max, "context_name", 0);

where timer_max denotes the maximum number of timers that will be used, "context_name" is the name of the default context and the last argument specifies the MPI-communicator to be used for this context (set to 0 in case of non-MPI src).

New timer and/or new context can be added by

new_timer = sct_new_timer("timer_name");

new_context = sct_new_context("context_name", comm);

The measurement of user-defined regions is done via

sct_start(timer_id);

sct_stop(timer_id);

Last timed interval can be shown

interval = sct_last_dt(timer_id);

and also the entire time taken by a timer

time = sct_val(timer_id);

The final report on all timers is given by

sct_report(proc_choice, thread_choice, sp_merging);

where

proc_choice describes a selection of MPI-tasks to be reported (see also below)
- integer task-id
- SCT_GET_ENV to use the envVar SCT_PROC_CHOICE
thread_choice describes a selection of OpenMP threads to be reported
- integer thread-id
- SCT_GET_ENV to use the envVar SCT_THREAD_CHOICE
sp_merging defines the merging strategy of serial and parallel OpenMP regions (see below)

Install

SCT uses autotools for the installation on your system. If you got the src from GIT-repo you need to have at least autoconf-2.69, automake 1.14 and libtool 2.4.2 installed. Produce a new configure script via:

autoreconf -fvi

If you downloaded the tar.gz file, you will already have the configure script, just use:

./configure
make
make check
make install

You can also specify several configure options, try –help for all details.

Controlling the output by environment variables

We support writing the measured timers to

stdout, stderr
ASCII file
HDF5 file (if compiled with support for HDF5)

Please use the folowing environment variables to control the output location:

SCT_OUT = [stdout | stderr | hdf5] (default: stdout)
SCT_FILENAME = <filename>

Reduction of timer results over several MPI-tasks and/or OpenMP-threads (showing min/max/avg) or complete output is done via

SCT_PROC_CHOICE = [SCT_SELECT_ALL | SCT_REDUCE_ALL | <proc_id>]
SCT_THREAD_CHOICE = [SCT_SELECT_ALL | SCT_REDUCE_ALL | <thread_id>] Combining serial phase measurement and parallel phase measurement (this only matters for OpenMP): SCT_SP_MERGING =
- SCT_SP_SERIAL_ONLY: only the serial phase measurement is used
- SCT_SP_PARALLEL_ONLY: only the thread-parallel measurement is used
- SCT_SP_MERGE_SIMPLE: the serial phase measurement is added to the master thread of parallel regions
- SCT_SP_SELECT_ALL: the serial phase measurement and the thread-parallel measurement are reported separately

Recording of eventcounters (if sct is installed with PAPI support)

SCT_EVENTCOUNTERS = [0 | 1 | 2] (default: 1) show counter results either as absolute values (1) or as rates per second (2)
SCT_EVENT_LIST: list of PAPI (or system specific) events to be recorded

Extended (showing statistics for each timer) or simple (showing only total sum for each timer) listing

SCT_CALLSTATS = [0 | 1] (default: 0)

Simple bookkeeping of timer hierarchy

SCT_NESTEDTIMERS = [0 | 1] (default: 0) , timer have to be nested correctly, hence this is not allowed:
sct_start(A);
sct_start(B);
...
<do some useful stuff>
...
sct_stop(A);
sct_stop(B)