| perf | |
|---|---|
| Repository | https://github.com/torvalds/linux/tree/master/tools/perf |
| Written in | C |
| Operating system | Linux kernel |
| Type | Performance monitor and testing |
| License | GNU GPL |
| Website | perf |
perf (sometimes calledperf_events[1] orperf tools, originallyPerformance Counters for Linux,PCL)[2] is aperformance analyzing tool inLinux, available fromLinux kernel version 2.6.31 in 2009.[3]Userspace controlling utility, namedperf, is accessed from thecommand line and provides a number ofsubcommands; it is capable of statistical profiling of the entire system (both kernel anduserland code).
It supportshardware performance counters,tracepoints, software performance counters (e.g. hrtimer), and dynamic probes (for example,kprobes or uprobes).[4] In 2012, twoIBM engineers recognized perf (along withOProfile) as one of the two most commonly usedperformance counter profiling tools on Linux.[5]
The interface between the perf utility and the kernel consists of only onesyscall and is done via afile descriptor and a mapped memory region.[6] UnlikeLTTng or older versions ofoprofile, no servicedaemons are needed, as most functionality is integrated into the kernel. The perf utility dumps raw data from the mapped buffer to disk when the buffer becomes filled up. According to R. Vitillo (LBNL), profiling performed by perf involves a very low overhead.[6]
As of 2010[update], architectures that provide support for hardware counters includex86,PowerPC64,UltraSPARC (III andIV),ARM (v5, v6, v7,Cortex-A8 and-A9),Alpha EV56 andSuperH.[4] Usage of Last Branch Records,[7] abranch tracing implementation available inIntel CPUs sincePentium 4, is available as a patch.[6] Since version 3.14 of theLinux kernel mainline, released on 31 March 2014, perf also supportsrunning average power limit (RAPL) for power consumption measurements, which is available as a feature of certain Intel CPUs.[8][9][10]
Perf is natively supported in many popular Linux distributions, includingRed Hat Enterprise Linux (since its version 6 released in 2010)[11] andDebian in thelinux-tools-common package (sinceDebian 6.0 (Squeeze) released in 2011).[12]
perf is used with several subcommands:
stat: measure total event count for single program or for system for some timetop:top-like dynamic view of hottest functionsrecord: measure and save sampling data for single program[13]report: analyze file generated by perf record; can generate flat, or graph profile.[13]annotate: annotate sources or assemblysched: tracing/measuring of scheduler actions and latencies[14]list: list available eventsThe documentation of perf is not very detailed (as of 2014); for example, it does not document most events or explain their aliases (often external tools are used to get names and codes of events[15]).[16] Perf tools also cannot profile based on true wall-clock time,[16] something that has been addressed by the addition of off-CPU profiling.
The perf subsystem of Linux kernels from 2.6.37 up to 3.8.8 and RHEL6 kernel 2.6.32 contained a security vulnerability (CVE-2013-2094), which was exploited to gain root privileges by a local user.[17][18] The problem was due to an incorrect type being used (32-bit int instead of 64-bit) in the event_id verification code path.[19]
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