[](https://crates.io/crates/curb)
[](https://travis-ci.com/jonhoo/curb)
A command-line tool to restrict a process from using particular hardware
resources. It is particularly geared towards performance-sensitive
multi-core experiments, in which you may want to avoid or measure the
impact of CPU features like [SMT] (e.g., [Intel Hyper-Threading] or
[NUMA memory]. While this is possible with existing tools like
[`hwloc-bind`] and [`numactl`], it's often pretty inconvenient to get
the result you want. With `curb` on the other hand:
```console
$ curb --no-smt --no-numa mycommand
```
You can also limit the number of cores using something like:
```console
$ curb --no-smt -n 3 mycommand
```
By default, curb picks cores, nodes, and anything else in a
deterministic fashion (usually tending towards 0). If you want to pick
randomly instead, use `--randomize` (or `-r`).
### Passing arguments
Will run `mycommand` _only_ on each physical core on a single NUMA node
(the first one specifically). Note that if you want to pass additional
arguments to the command under test, you can do so using `--`:
```console
$ curb --no-smt mycommand -- --no-crash --performance better
```
### Visualizing the core allocation
To visualize what CPUs are being used using [`lstopo`], do:
```console
$ curb --no-smt --no-numa lstopo -- --pid 0
```
That should show all active cores in green. If you don't have a window
manager running, add `-v` at the end and look for PUs marked with
`(running)`.
## Dependencies
Curb depends on the [`hwloc` crate], which in turn depends on the
[`hwloc` C library].
## OS Support
Curb currently only works on `cfg(unix)` systems, because it sets the
CPU binding [for the current process], and then calls [`exec`]. This
should be possible to work around by instead spawning the process,
getting its identifier, calling [`set_cpubind_for_process`], and then
waiting for the process to exit. However, this has a number of
downsides, like the process _initially_ being unconstrained and having
to proxy things like stdin, stdout, signals, and exit codes. Suggestions
for how to support non-UNIX platforms are warmly welcome!
[SMT]: https://en.wikipedia.org/wiki/Simultaneous_multithreading
[Intel Hyper-Threading]: https://en.wikipedia.org/wiki/Hyper-threading
[NUMA memory]: https://en.wikipedia.org/wiki/Non-uniform_memory_access
[`hwloc-bind`]: https://linux.die.net/man/1/hwloc-bind
[`numactl`]: https://github.com/numactl/numactl
[`lstopo`]: https://linux.die.net/man/1/lstopo
[`hwloc` crate]: https://github.com/daschl/hwloc-rs
[`hwloc` C library]: https://github.com/daschl/hwloc-rs#prerequisites
[for the current process]: https://docs.rs/hwloc/0.5.0/hwloc/struct.Topology.html#method.set_cpubind
[`exec`]: https://doc.rust-lang.org/std/os/unix/process/trait.CommandExt.html#tymethod.exec
[`set_cpubind_for_process`]: https://docs.rs/hwloc/0.5.0/hwloc/struct.Topology.html#method.set_cpubind_for_process