timer command

Syntax

timer args
  • args = one or more of off or loop or normal or full or sync or nosync or timeout or every
off = do not collect or print any timing information
loop = collect only the total time for the simulation loop
normal = collect timer information broken down by sections (default)
full = like normal but also include CPU and thread utilization
sync = explicitly synchronize MPI tasks between sections
nosync = do not synchronize MPI tasks between sections (default)
timeout elapse = set walltime limit to elapse
every Ncheck = perform timeout check every Ncheck steps

Examples

timer full sync
timer timeout 2:00:00 every 100
timer loop

Description

Select the level of detail at which LAMMPS performs its CPU timings. Multiple keywords can be specified with the timer command. For keywords that are mutually exclusive, the last one specified takes precedence.

During a simulation run LAMMPS collects information about how much time is spent in different sections of the code and thus can provide information for determining performance and load imbalance problems. This can be done at different levels of detail and accuracy. For more information about the timing output, see this discussion of screen output in Section 2.8.

The off setting will turn all time measurements off. The loop setting will only measure the total time for a run and not collect any detailed per section information. With the normal setting, timing information for portions of the timestep (pairwise calculations, neighbor list construction, output, etc) are collected as well as information about load imbalances for those sections across processors. The full setting adds information about CPU utilization and thread utilization, when multi-threading is enabled.

With the sync setting, all MPI tasks are synchronized at each timer call which measures load imbalance for each section more accurately, though it can also slow down the simulation by prohibiting overlapping independent computations on different MPI ranks Using the nosync setting (which is the default) turns this synchronization off.

With the timeout keyword a walltime limit can be imposed, that affects the run and minimize commands. This can be convenient when calculations have to comply with execution time limits, e.g. when running under a batch system when you want to maximize the utilization of the batch time slot, especially for runs where the time per timestep varies much and thus it becomes difficult to predict how many steps a simulation can perform for a given walltime limit. This also applies for difficult to converge minimizations. The timeout elapse value should be somewhat smaller than the maximum wall time requested from the batch system, as there is usually some overhead to launch jobs, and it is advisable to write out a restart after terminating a run due to a timeout.

The timeout timer starts when the command is issued. When the time limit is reached, the run or energy minimization will exit on the next step or iteration that is a multiple of the Ncheck value which can be set with the every keyword. Default is checking every 10 steps. After the timer timeout has expired all subsequent run or minimize commands in the input script will be skipped. The remaining time or timer status can be accessed with the thermo variable timeremain, which will be zero, if the timeout is inactive (default setting), it will be negative, if the timeout time is expired and positive if there is time remaining and in this case the value of the variable are the number of seconds remaining.

When the timeout key word is used a second time, the timer is restarted with a new time limit. The timeout elapse value can be specified as off or unlimited to impose a no timeout condition (which is the default). The elapse setting can be specified as a single number for seconds, two numbers separated by a colon (MM:SS) for minutes and seconds, or as three numbers separated by colons for hours, minutes, and seconds (H:MM:SS).

The every keyword sets how frequently during a run or energy minimization the wall clock will be checked. This check count applies to the outer iterations or time steps during minimizations or r-RESPA runs, respectively. Checking for timeout too often, can slow a calculation down. Checking too infrequently can make the timeout measurement less accurate, with the run being stopped later than desired.

Note

Using the full and sync options provides the most detailed and accurate timing information, but can also have a negative performance impact due to the overhead of the many required system calls. It is thus recommended to use these settings only when testing tests to identify performance bottlenecks. For calculations with few atoms or a very large number of processors, even the normal setting can have a measurable negative performance impact. In those cases you can just use the loop or off setting.

Restrictions

none

Default

timer normal nosync
timer timeout off
timer every 10