57 lines
2.6 KiB
Markdown
57 lines
2.6 KiB
Markdown
# Environment variables
|
||
|
||
Some environment variables can be used to adjust settings during the execution
|
||
of libovni, they all begin with the `OVNI_` prefix. Be sure that all threads of
|
||
the same node use the same environment variables.
|
||
|
||
## OVNI_TMPDIR
|
||
|
||
During the execution of your program, a per-thread buffer is kept where the new
|
||
events are being recorded. When this buffer is full, it is written to disk and
|
||
emptied, an operation known as flush. This may take a while depending on the
|
||
underlying filesystem.
|
||
|
||
Keep in mind that the thread will be blocked until the flush ends, so if your
|
||
filesystem is slow it would interrupt the execution of your program for a long
|
||
time. It is advisable to use the fastest filesystem available (see the tmpfs(5)
|
||
and df(1) manual pages).
|
||
|
||
You can select a temporary trace directory where the buffers will be flushed
|
||
during the execution by setting the environment variable `OVNI_TMPDIR`. The last
|
||
directory will be created if doesn't exist. In that case, as soon as a process
|
||
calls `ovni_proc_fini()`, the traces of all its threads will be moved to the
|
||
final directory at `$PWD/ovni`. Example:
|
||
|
||
OVNI_TMPDIR=$(mktemp -u /dev/shm/ovni.XXXXXX) srun ./your-app
|
||
|
||
To test the different filesystem speeds, you can use hyperfine and dd. Take a
|
||
closer look at the max time:
|
||
|
||
```
|
||
$ hyperfine 'dd if=/dev/zero of=/gpfs/projects/bsc15/bsc15557/kk bs=2M count=10'
|
||
Benchmark 1: dd if=/dev/zero of=/gpfs/projects/bsc15/bsc15557/kk bs=2M count=10
|
||
Time (mean ± σ): 71.7 ms ± 130.4 ms [User: 0.8 ms, System: 10.2 ms]
|
||
Range (min … max): 14.7 ms … 1113.2 ms 162 runs
|
||
|
||
Warning: Statistical outliers were detected. Consider re-running this
|
||
benchmark on a quiet PC without any interferences from other programs. It
|
||
might help to use the '--warmup' or '--prepare' options.
|
||
|
||
$ hyperfine 'dd if=/dev/zero of=/tmp/kk bs=2M count=10'
|
||
Benchmark 1: dd if=/dev/zero of=/tmp/kk bs=2M count=10
|
||
Time (mean ± σ): 56.2 ms ± 5.7 ms [User: 0.6 ms, System: 14.8 ms]
|
||
Range (min … max): 45.8 ms … 77.8 ms 63 runs
|
||
|
||
$ hyperfine 'dd if=/dev/zero of=/dev/shm/kk bs=2M count=10'
|
||
Benchmark 1: dd if=/dev/zero of=/dev/shm/kk bs=2M count=10
|
||
Time (mean ± σ): 11.4 ms ± 0.4 ms [User: 0.5 ms, System: 11.1 ms]
|
||
Range (min … max): 9.7 ms … 12.5 ms 269 runs
|
||
```
|
||
|
||
## OVNI_TRACEDIR
|
||
|
||
By default, the runtime trace will be placed in the `ovni` directory, inside the
|
||
working directory. You can specify a different location to place the trace by
|
||
setting the `OVNI_TRACEDIR` environment variable. It accepts a relative or
|
||
absolute path, which will be created if it doesn't exist.
|