The Tool Desk
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When an RDMA workload makes a network device busy, rdmatop gives Linux operators an interactive view of device traffic and selected RDMA counters, with an attempt to associate queue pairs with local processes. It is a terminal monitor—not an application benchmark or a general-purpose network monitor—and requires an RDMA-capable NIC.
What rdmatop shows
The rdmatop project describes the tool as “htop, but for RDMA traffic.” Its terminal interface reports per-device throughput in Gbps and packets per second, drops, RDMA read and write counters, retransmits, and health events. It also displays processes associated with RDMA devices where it can map queue pairs to local process information. These are capabilities described by the project, not results from independent testing.
This makes rdmatop useful for an operational question such as which RDMA device is active during a communication workload. The project names NCCL, NVSHMEM, UCX Perftest, IB Perftest, and NIXL as contexts for using the monitor. Seeing traffic while one of those workloads runs does not mean rdmatop measures that workload’s benchmark performance.
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What you need to run it
- Linux: rdmatop uses Linux RDMA netlink and does not support macOS or Windows.
- An RDMA-capable NIC: Project examples include NVIDIA/Mellanox ConnectX and AWS EFA. They are examples, not a complete compatibility list.
The project documentation does not establish a provider-by-provider support matrix for counters, kernel and driver versions, or required privileges. Counter availability and process mapping may therefore differ by device and software stack; confirm behavior on the host you intend to monitor.
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How it gathers and calculates information
According to the project README, rdmatop uses Linux RDMA netlink to enumerate devices with RDMA_NLDEV_CMD_GET and retrieve hardware statistics with RDMA_NLDEV_CMD_STAT_GET, the interface used by rdma statistic show. For process attribution, it queries queue-pair resources using RDMA_NLDEV_CMD_RES_QP_GET and enriches that information with data from /proc.
For rates, the tool compares successive counter snapshots and divides the change by the elapsed time. A displayed rate is therefore a calculated rate over the interval between observations, rather than a direct measurement of an application’s end-to-end performance. This describes the implementation documented by the project; it is not an independent audit of the tool’s measurements.
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Install and start rdmatop
The project documents three installation routes. Its README is the place to confirm the current commands and distribution availability, which can change.
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- Cargo: Install with
cargo install rdmatop, as documented by the project. - Build from source: Use the Makefile instructions in the repository.
After installation, run rdmatop in a terminal to open the interface. The package page surfaced for version 0.1.32 lists a release date of 2026-10-02; that is a time-specific package listing, not a guarantee that the version will remain current. See the Docs.rs package page for its latest listing.
Record a trace for later inspection
While rdmatop is running, press r to start recording and press r again to stop. The project says it writes a Chrome JSON trace in the current directory that can be opened with Perfetto. The output filename may vary with the installed release, so check the resulting file in that directory rather than assuming a fixed name. For the key sequence and current behavior, consult the project README.
What its output can—and cannot—tell you
rdmatop is best understood as a live, device-oriented inspection aid. It can help show which device has traffic and expose selected counters while a workload is running. It does not, by itself, establish why a workload is slow, validate performance against an external reference, or provide a complete view of every provider’s counters. The project documentation does not specify measurement overhead, universal counter coverage, or compatibility across every kernel and driver combination.
Before relying on a particular counter or process association in an operational investigation, verify that it appears and behaves as expected on the target host. The project’s overview, “rdmatop: Cross-Provider htop for RDMA Traffic”, provides additional project context, but does not replace checking the behavior of the local RDMA stack.
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