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Rezolus is a tool for collecting detailed systems performance telemetry and exposing burst patterns through high-resolution telemetry. Rezolus provides instrumentation of basic systems metrics, performance counters, and support for eBPF (extended Berkeley Packet Filter) telemetry. Measurement is the first step toward improved performance.

Per-metric documentation can be found in the METRICS documentation.


Rezolus collects telemetry from several different sources. Currently, Rezolus collects telemetry from traditional sources (procfs, sysfs), the perf_events subsystem, and from BPF. Each sampler implements a consistent set of functions so that new ones can be easily added to further extend the capabilities of Rezolus.

Each telemetry source is oversampled so that we can build a histogram across a time interval. This histogram allows us to capture variations which will appear in the far upper and lower percentiles. This oversampling approach is one of the key differentiators of Rezolus when compared to other telemetry agents.

With its support for BPF as well as more common telemetry sources, Rezolus is a very sophisticated tool for capturing performance anomalies, profiling systems performance, and conducting performance diagnostics.

More detailed information about the underlying metrics library and sampler design can be found in the DESIGN documentation.


  • traditional telemetry sources (procfs, sysfs, ...)
  • perf_events support for hardware performance counters
  • BPF support to instrument kernel and user space activities
  • oversampling and percentile metrics to capture bursts

Traditional Telemetry Sources

Rezolus collects metrics from traditional sources (procfs, sysfs) to provide basic telemetry for CPU, disk, and network. Rezolus exports CPU utilization, disk bandwidth, disk IOPs, network bandwidth, network packet rate, network errors, as well as TCP and UDP protocol counters.

These basic telemetry sources, when coupled with the approach of oversampling to capture their bursts, often provide a high-level view of systems performance and may readily indicate areas where resources are saturated or errors are occurring.

Perf Events

Perf Events allow us to report on both hardware and software events. Typical software events are things like page faults, context switches, and CPU migrations. Typical hardware events are things like CPU cycles, instructions retired, cache hits, cache misses, and a variety of other detailed metrics about how a workload is running on the underlying hardware.

These metrics are typically used for advanced performance debugging, as well as for tuning and optimization efforts.


There is an expansive amount of performance information that can be exposed through BPF, which allows us to have the Linux Kernel perform telemetry capture and aggregation at very fine-grained levels.

Rezolus comes with samplers that capture block IO size distribution, EXT4 and XFS operation latency distribution, and scheduler run queue latency distribution. You'll see that here we are mainly exposing distributions of sizes and latencies The kernel is recording the appropriate value for each operation into a histogram. Rezolus then accesses this histogram from user-space and transfers the values over to its own internal storage where it is then exposed to external aggregators.

By collecting telemetry in-kernel, we're able to gather data about events that happen at extremely high rates - e.g., task scheduling - with minimal performance overhead for collecting the telemetry. The BPF samplers can be used to both capture runtime performance anomalies as well as characterize workloads.

Sampling rate and resolution

In order to accurately reflect the intensity of a burst, the sampling rate must be at least twice the duration of the shortest burst to record accurately. This ensures that at least 1 sample completely overlaps the burst section of the event. With a traditional minutely time series, this means that a spike must least 120 seconds or more to be accurately recorded in terms of intensity. Rezolus allows for sampling rate to be configured, allowing us to make a trade-off between resolution and resource consumption. At 10Hz sampling, 200ms or more of consecutive burst is enough to be accurately reflected in the pMax. Contrast that with minutely metrics requiring 120_000ms, or secondly requiring 2000ms of consecutive burst to be accurately recorded.

Getting Started


Rezolus is built with the standard Rust toolchain which can be installed and managed via rustup or by following the directions on the Rust website.

NOTE: at this time, Rezolus needs to be built with the nightly toolchain or a locally built development toolchain which has nightly features enabled. This is because Rezolus requires language features that have not been fully stabilized in the language. These features are required to get support for performance counters.

The rest of the guide assumes you've chosen to install the toolchain via rustup.

NOTE: Rezolus is intended to be built and deployed on Linux systems.

Clone and build Rezolus from source

git clone
cd rezolus

# create an unoptimized development build
cargo build

# run the unoptimized binary and display help
cargo run -- --help

# create an optimized release build
cargo build --release

# run the optimized binary and display help
cargo run --release -- --help

# run the optimized binary with the example config (needs sudo for perf_events)
cargo build --release && \
sudo target/release/rezolus --config configs/example.toml

# metrics can be viewed in human-readable form with curl
curl --silent http://localhost:4242/vars

Building with BPF Support

By default, BPF support is not compiled in. If you wish to produce a build with BPF support enabled, follow the steps below:


BPF support requires that we link against the BPF Compiler Collection. You may either use the version provided by your distribution, or can build BCC and install from source. It is critical to know which version of BCC you have installed. Rezolus supports multiple versions by utilizing different feature flags at build time.

Our current policy is to support BCC versions back to the version in the distribution repository for Debian Stable or CentOS 7 (whichever is older) to the most recent version of BCC.

This policy provides coverage for current stable and testing versions of Debian, Ubuntu, CentOS, Fedora, Arch, and Gentoo. Users of other distributions may need to build a supported version of BCC from source. See BCC Installation Guide for details.


As mentioned above, we provide different feature flags to map to various supported BCC versions. The bpf feature will map to the newest version supported by the rust-bcc project. For most users, this will be the right flag to use. However, if you must link against an older BCC version, you will need to use a more specific form of the feature flag. These version-specific flags take the form of bpf_v0_10_0 with the BCC version being reflected in the name of the feature. You can find a complete list of the feature flags in the cargo manifest for this project.

# create an optimized release build with BPF support
cargo build --release --features bpf
sudo target/release/rezolus --config configs/example.toml

# metrics can be viewed in human-readable form with curl
curl --silent http://localhost:4242/vars

HTTP Exposition

Rezolus exposes metrics over HTTP, with different paths corresponding to different exposition formats.

  • human-readable: /vars
  • JSON: /vars.json, /metrics.json, /admin/metrics.json
  • Prometheus: /metrics

NOTE: currently, JSON exposition is provided by default for any other path. This behavior may change in the future and should not be relied on.

Additionally, you can get the running version on the root-level path /


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