# 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*

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    *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 wall time limit to *elapse*
    *every* Ncheck = perform timeout check every *Ncheck* steps

## Examples

``` LAMMPS
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 the [Run output](Run_output)
doc page.

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 wall time limit can be imposed, that
affects the [run](run) and [minimize](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 wall time 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](thermo_style) 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](run_style), 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
::: title
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

## Related commands

[run post no](run), [kspace_modify fftbench](kspace_modify)

## Default

``` LAMMPS
timer normal nosync
timer timeout off
timer every 10
```