perf (sometimes called perf_eventsVince Weaver, The Unofficial Linux Perf Events Web-Page or perf tools, originally Performance Counters for Linux, PCL)Linux perf event Features and Overhead // 2013 FastPath Workshop, Vince Weaver is a performance analyzing tool in Linux, available from Linux kernel version 2.6.31 in 2009.Jake Edge, Perfcounters added to the mainline, LWN July 1, 2009, "perfcounters being included into the mainline during the recently completed 2.6.31 merge window" Userspace controlling utility, named perf, is accessed from the command line and provides a number of subcommands; it is capable of statistical profiling of the entire system (both kernel and userland code).
It supports hardware performance counters, tracepoints, software performance counters (e.g. hrtimer), and dynamic probes (for example, kprobes or uprobes). In 2012, two IBM engineers recognized perf (along with OProfile) as one of the two most commonly used performance counter profiling tools on Linux.A. Zanella, R. Arnold. Evaluate performance for Linux on POWER. Analyze performance using Linux tools, 12 Jun 2012 // IBM DeveloperWorks Technical library
Implementation The interface between the perf utility and the kernel consists of only one syscall and is done via a file descriptor and a mapped memory region.Roberto A. Vitillo (LBNL). PERFORMANCE TOOLS DEVELOPMENTS, 16 June 2011, presentation from "Future computing in particle physics" conference Unlike LTTng or older versions of oprofile, no service daemons 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.
, architectures that provide support for hardware counters include x86, PowerPC64, UltraSPARC (III and IV), ARM (v5, v6, v7, Cortex-A8 and -A9), Alpha EV56 and SuperH.Arnaldo Carvalho de Melo, The New Linux ’perf’ tools, presentation from Linux Kongress, September, 2010 Usage of Last Branch Records, a branch tracing implementation available in Intel CPUs since Pentium 4, is available as a patch. Since version 3.14 of the Linux kernel mainline, released on 31 March 2014, perf also supports running average power limit (RAPL) for power consumption measurements, which is available as a feature of certain Intel CPUs.
Perf is natively supported in many popular Linux distributions, including Red Hat Enterprise Linux (since its version 6 released in 2010)6.4. Performance Counters for Linux (PCL) Tools and perf // RHEL Developer Guide and Debian in the linux-tools-common package (since Debian 6.0 (Squeeze) released in 2011).
Subcommands perf is used with several subcommands: stat: measure total event count for single program or for system for some time top: top-like dynamic view of hottest functions record: measure and save sampling data for single programUrs Fässler perf file format , CERN openlab, 2011 report: analyze file generated by perf record; can generate flat, or graph profile. annotate: annotate sources or assembly sched: tracing/measuring of scheduler actions and latenciesIngo Molnar, 'perf sched': Utility to capture, measure and analyze scheduler latencies and behavior, 17 Sep 2009 list: list available events
Criticism The 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 eventsHow to monitor the full range of CPU performance events // Bojan Nikolic, 2012). Perf tools also cannot profile based on true wall-clock time,Robert Haas (PostgreSQL), perf: the good, the bad, the ugly // 6 June 2012 something that has been addressed by the addition of off-CPU profiling.
Security 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 (), which was exploited to gain root privileges by a local user. The problem was due to an incorrect type being used (32-bit int instead of 64-bit) in the event_id verification code path.
See also List of performance analysis tools OProfile Performance Application Programming Interface Profiling (computer programming)
References
External links perf's wiki on kernel.org Arnaldo Carvalho de Melo, The New Linux ’perf’ tools, presentation from Linux Kongress, September, 2010 Hardware PMU support charts – check perf_event column