1 unstable release
0.1.0 | Jun 17, 2024 |
---|
#125 in Profiling
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47KB
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[cargo-]cbench
Environment control for benchmarks on Linux/systemd, reducing external noise from benchmark results.
cbench
can be used to run any programs. cargo-cbench
is a wrapper giving a
cargo bench
-like interface for running cargo benches conveniently.
Installation
cargo install cbench
Usage
For Rust projects with cargo benches, simply replace cargo bench
with
cargo cbench
:
cargo cbench
This will setup the environment and tweak system configurables (see the next section), run all cargo benchmarks in the current project, and finally revert changes to the original state.
It will only allocate a single exclusive CPU for the benchmark. If your program is multi-threaded, you can allocate more by:
cargo cbench --cpus=1-2
Cargo flags and bench program flags can be passed using the same syntax:
cargo cbench --bench=bench1 --features=feat1 -- --exact foo
For other benchmarking frameworks, run cbench
following by the command:
cbench hyperfine /some/benchee
By default, the target command will be run inside a systemd unit named
'cbench.service' as the current user. It will be in a clean environment
without inheriting from the current shell. If your command relies on some
environment variables, you need to pass them explicitly via --setenv=ENV
or
--setenv=ENV=VALUE
.
More control arguments can be seen in cbench --help
.
What it does
noaslr
: Disable Address Space Layout Randomization (ASLR) via/proc/sys/kernel/randomize_va_space
cpuset
: Pin the target process' cgroup on specific CPU(s) for exclusive use via cgroup cpuset.noht
: Disable (set offline) CPU thread siblings of the CPU(s) used if hyper-threading is enabled, via CPU hotplug.cpufreq
: Set power governor of target CPU(s) to 'performance' and disable adaptive turbo/boost, via CPU Performance Scaling.noirq
: Mask used CPU(s) from IRQ affinity.
These control modules can be enabled or disabled individually via --with=
or
--without=
.
What it does NOT
-
We don't do benchmarks, but we setup environment and tunables for benchmark programs to do benchmarks more reliably. It's expected to be used together with benchmark frameworks/programs like
criterion
orhyperfine
. -
Environment control does not make programs run faster, but typically in opposite, because we disable frequency boost by default. Our goal is consistency rather than performance.
-
We reduce external noise from tainting the benchmark results. But we cannot magically stabilize it from internal biases. Benchee may still be unstable under different memory (heap and stack) layout caused by environment variables or "being lucky" on program initialization, producing a seemingly random systemic bias through multiple runs. You need to carefully write your benchee program to reduce this effect.
See stabilizer for more information.
Privileged operations
All settings mentioned above are privileged and machine global. To minimize the
impact and security risks, we leverage systemd-run
privileged
ExecStartPre=
/ExecStopPost=
commands, thus only the environment setup and
reset will be executed with root privileges. Authentication is done by
systemd-run
itself by default (via PolKit), or you can use --use-sudo
to
use sudo
instead.
Note that no matter whether --use-sudo
is used, the program compilation (via
cargo build
) and benchmark processes are always running as the current user.
Never add sudo
to cargo cbench
itself! Even if you really want to run the
target artifact/command as root
because, say you are running perf stat --all-kernel
, use the option --root
for it.
Environment modifications will be reverted after the program exits via systemd
ExecStopPost=
command, which will do the clean up even if the target process
aborted unexpectedly (eg. by Ctrl-C). If they do not, please report a bug.
Credit
- Heavily motivated by LLVM benchmarking tips.
- Thank QuarticCat@github for turbo/boost control tips.
- Thank PeterCxy@github for IRQ control tips.
Dependencies
~5–31MB
~472K SLoC