perf: Linux profiling with performance counters
...More than just counters...
This is the wiki page for the Linux perf command, also called perf_events. perf is powerful: it can instrument CPU performance counters, tracepoints, kprobes, and uprobes (dynamic tracing). It is capable of lightweight profiling. It is also included in the Linux kernel, under tools/perf, and is frequently updated and enhanced.
perf began as a tool for using the performance counters subsystem in Linux, and has had various enhancements to add tracing capabilities.
Performance counters are CPU hardware registers that count hardware events such as instructions executed, cache-misses suffered, or branches mispredicted. They form a basis for profiling applications to trace dynamic control flow and identify hotspots. perf provides rich generalized abstractions over hardware specific capabilities. Among others, it provides per task, per CPU and per-workload counters, sampling on top of these and source code event annotation.
Tracepoints are instrumentation points placed at logical locations in code, such as for system calls, TCP/IP events, file system operations, etc. These have negligible overhead when not in use, and can be enabled by the perf command to collect information including timestamps and stack traces. perf can also dynamically create tracepoints using the kprobes and uprobes frameworks, for kernel and userspace dynamic tracing. The possibilities with these are endless.
The userspace perf command present a simple to use interface with commands like:
- perf stat: obtain event counts
- perf record: record events for later reporting
- perf report: break down events by process, function, etc.
- perf annotate: annotate assembly or source code with event counts
- perf top: see live event count
- perf bench: run different kernel microbenchmarks
To learn more, see the examples in the Tutorial.
- perf_events kernel ABI
- perf tools support for Intel® Processor Trace
- Roberto Vitillo's presentation on Perf events
- Brendan Gregg's perf examples
- CppCon 2015: Chandler Carruth "Tuning C++: Benchmarks, and CPUs, and Compilers! Oh My!"
- Mark Dawson, Jr. uses 'perf diff' on "5-level vs 4-level Page Tables: Does It Matter?"
- Joe Mario's original 2016 article about 'perf c2c' "C2C - False Sharing Detection in Linux Perf"
- Leo Yan on supporting 'perf c2c' on Armv8.2 "Using the Arm Statistical Profiling Extension to detect false cache-line sharing"
- Franck Pachot's not so basic perf top tutorial "Linux perf-top basics: understand the %"
- Frank Pachot help going from 'time' to 'perf stat' while analysing database performance on "Should CPU-intensive logic be done in the DB or in application server?"