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(References/Useful links: Added link to Chandler's talk at CppCon2015 where he uses perf a lot!)
 
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<big>'''Performance Counters for Linux Wiki'''</big>
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== <tt>perf:</tt> Linux profiling with performance counters ==
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''...More than just counters...''
  
This is the wiki page for the perfcounters subsystem in Linux.
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=== Introduction ===
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This is the wiki page for the Linux <tt>perf</tt> command, also called perf_events. <tt>perf</tt> 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.
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<tt>perf</tt> began as a tool for using the performance counters subsystem in Linux, and has had various enhancements to add tracing capabilities.
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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. <tt>perf</tt> 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.
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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 <tt>perf</tt> command to collect information including timestamps and stack traces. <tt>perf</tt> can also dynamically create tracepoints using the kprobes and uprobes frameworks, for kernel and userspace dynamic tracing. The possibilities with these are endless.
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The userspace <tt>perf</tt> command present a simple to use interface with commands like:
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* <tt>[[Tutorial#Counting_with_perf_stat| perf stat</tt>]]: obtain event counts
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* <tt>[[Tutorial#Sampling_with_perf_record | perf record</tt>]]: record events for later reporting
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* <tt>[[Tutorial#Sample_analysis_with_perf_report | perf report</tt>]]: break down events by process, function, etc.
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* <tt>[[Tutorial#Source_level_analysis_with_perf_annotate | perf annotate</tt>]]: annotate assembly or source code with event counts
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* <tt>[[Tutorial#Live_analysis_with_perf_top | perf top</tt>]]: see live event count
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* <tt>[[Tutorial#Benchmarking_with_perf_bench | perf bench</tt>]]: run different kernel microbenchmarks
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To learn more, see the examples in the [[Tutorial]].
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=== Wiki Contents  ===
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* [[Tutorial]]
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* [[Todo]]
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* [[HardwareReference]]
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* [[perf_events kernel ABI]]
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=== References/Useful links ===
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* [http://indico.cern.ch/materialDisplay.py?contribId=20&sessionId=4&materialId=slides&confId=141309 Roberto Vitillo's presentation on Perf events]
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* [http://www.brendangregg.com/perf.html Brendan Gregg's perf examples]
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* [https://youtu.be/nXaxk27zwlk CppCon 2015: Chandler Carruth "Tuning C++: Benchmarks, and CPUs, and Compilers! Oh My!"]

Latest revision as of 14:33, 28 September 2015

Contents

[edit] perf: Linux profiling with performance counters

...More than just counters...

[edit] Introduction

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:

To learn more, see the examples in the Tutorial.

[edit] Wiki Contents

[edit] References/Useful links

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