perf (sometimes called perf_events or perf tools, originally Performance Counters for Linux, PCL) is a performance analyzing tool in Linux, available from Linux kernel version 2.6.31 in 2009. 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).
|Operating system||Linux kernel|
|Type||Performance monitor and testing|
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.
The interface between the perf utility and the kernel consists of only one syscall and is done via a file descriptor and an mapped memory region. 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.
As of 2010, 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. 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 March 31, 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) and Debian in linux-tools-common package (since its Squeeze version released in 2011).
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 program
- 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 latencies
- list: list available events
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 events). Perf tools also cannot profile based on true wall-clock time.
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. The problem was due to an incorrect type being used (32-bit int instead of 64-bit) in the event_id verification code path.
- Vince Weaver, The Unofficial Linux Perf Events Web-Page
- Linux perf event Features and Overhead // 2013 FastPath Workshop, Vince Weaver
- 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"
- Arnaldo Carvalho de Melo, The New Linux ’perf’ tools, presentation from Linux Kongress, September, 2010
- A. Zanella, R. Arnold. Evaluate performance for Linux on POWER. Analyze performance using Linux tools, 12 Jun 2012 // IBM DeveloperWorks Technical library
- Roberto A. Vitillo (LBNL). PERFORMANCE TOOLS DEVELOPMENTS, 16 June 2011, presentation from "Future computing in particle physics" conference
- Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3B: System Programming Guide, Part 2. Intel. June 2009. p. 19-2 vol. 3.
- Jake Edge (2014-04-09). "Lots of new perf features". LWN.net. Retrieved 2014-04-22.
- Jacob Pan (2013-04-02). "RAPL (Running Average Power Limit) driver". LWN.net. Retrieved 2014-04-22.
- "kernel/git/torvalds/linux.git - Linux kernel source tree". Git.kernel.org. 2014-01-20. Retrieved 2014-03-31.
- 6.4. Performance Counters for Linux (PCL) Tools and perf // RHEL Developer Guide
- "Debian - Details of package linux-tools-2.6.32 in squeeze". Packages.debian.org. Retrieved 2014-03-31.
- Urs Fässler perf file format, CERN OpenLab, 2011
- Ingo Molnar, 'perf sched': Utility to capture, measure and analyze scheduler latencies and behavior, 17 Sep 2009
- How to monitor the full range of CPU performance events // Bojan Nikolic, 2012
- Robert Haas (PostgreSQL), perf: the good, the bad, the ugly // June 06, 2012
- Michael Larabel (2013-05-15). "New Linux Kernel Vulnerability Exploited". Phoronix.
- corbet (2013-05-15). "Local root vulnerability in the kernel". LWN.
- Joe Damato (2013-05-20). "A closer look at a recent privilege escalation bug in Linux (CVE-2013-2094)".