A miscellaneous collection of in-development and unsupported performance analysis tools for Linux ftrace and perf_events (aka the "perf" command). Both ftrace and perf are core Linux tracing tools, included in the kernel source. Your system probably has ftrace already, and perf is often just a package add (see Prerequisites).
These tools are designed to be easy to install (fewest dependencies), provide advanced performance observability, and be simple to use: do one thing and do it well. This collection was created by Brendan Gregg (author of the DTraceToolkit).
Many of these tools employ workarounds so that functionality is possible on existing Linux kernels. Because of this, many tools have caveats (see man pages), and their implementation should be considered a placeholder until future kernel features, or new tracing subsystems, are added.
These are intended for Linux 3.2 and newer kernels. For Linux 2.6.x, see Warnings.
Presentation
These tools were introduced in the USENIX LISA 2014 presentation: Linux Performance Analysis: New Tools and Old Secrets
Contents
Using ftrace:
Using perf_events:
Using eBPF:
- As a preview of things to come, see the bcc tracing Tools section. These use bcc, a front end for using eBPF. bcc+eBPF will allow some of these tools to be rewritten and improved, and additional tools to be created.
Screenshots
Showing new processes and arguments:
# ./execsnoop
Tracing exec()s. Ctrl-C to end.
PID PPID ARGS
22898 22004 man ls
22905 22898 preconv -e UTF-8
22908 22898 pager -s
22907 22898 nroff -mandoc -rLL=164n -rLT=164n -Tutf8
22906 22898 tbl
22911 22910 locale charmap
22912 22907 groff -mtty-char -Tutf8 -mandoc -rLL=164n -rLT=164n
22913 22912 troff -mtty-char -mandoc -rLL=164n -rLT=164n -Tutf8
22914 22912 grotty
Measuring block device I/O latency from queue insert to completion:
# ./iolatency -Q
Tracing block I/O. Output every 1 seconds. Ctrl-C to end.
>=(ms) .. <(ms) : I/O |Distribution |
0 -> 1 : 1913 |######################################|
1 -> 2 : 438 |######### |
2 -> 4 : 100 |## |
4 -> 8 : 145 |### |
8 -> 16 : 43 |# |
16 -> 32 : 43 |# |
32 -> 64 : 1 |# |
[...]
Tracing the block:block_rq_insert tracepoint, with kernel stack traces, and only for reads:
# ./tpoint -s block:block_rq_insert 'rwbs ~ "*R*"'
cksum-11908 [000] d... 7269839.919098: block_rq_insert: 202,1 R 0 () 736560 + 136 [cksum]
cksum-11908 [000] d... 7269839.919107:
=> __elv_add_request
=> blk_flush_plug_list
=> blk_finish_plug
=> __do_page_cache_readahead
=> ondemand_readahead
=> page_cache_async_readahead
=> generic_file_read_iter
=> new_sync_read
=> vfs_read
=> SyS_read
=> system_call_fastpath
[...]
Count kernel function calls beginning with "bio_", summarize every second:
# ./funccount -i 1 'bio_*'
Tracing "bio_*"... Ctrl-C to end.
FUNC COUNT
bio_attempt_back_merge 26
bio_get_nr_vecs 361
bio_alloc 536
bio_alloc_bioset 536
bio_endio 536
bio_free 536
bio_fs_destructor 536
bio_init 536
bio_integrity_enabled 536
bio_put 729
bio_add_page 1004
[...]
There are many more examples in the examples directory. Also see the man pages.
Prerequisites
The intent is as few as possible. Eg, a Linux 3.2 server without debuginfo. See the tool man page for specifics.
ftrace
FTRACE configured in the kernel. You may already have this configured and available in your kernel version, as FTRACE was first added in 2.6.27. This requires CONFIG_FTRACE and other FTRACE options depending on the tool. Some tools (eg, funccount) require CONFIG_FUNCTION_PROFILER.
perf_events
Requires the "perf" command to be installed. This is in the linux-tools-common package. After installing that, perf may tell you to install an additional linux-tools package (linux-tools-kernel_version). perf can also be built under tools/perf in the kernel source. See perf_events Prerequisites for more details about getting perf_events to work fully.
debugfs
Requires a kernel with CONFIG_DEBUG_FS option enabled. As with FTRACE, this may already be enabled (debugfs was added in 2.6.10-rc3). The debugfs also needs to be mounted:
# mount -t debugfs none /sys/kernel/debug
awk
Many of there scripts use awk, and will try to use either mawk or gawk depending on the desired behavior: mawk for buffered output (because of its speed), and gawk for synchronous output (as fflush() works, allowing more efficient grouping of writes).
Install
These are just scripts. Either grab everything:
git clone --depth 1 https://github.com/brendangregg/perf-tools
Or use the raw links on github to download individual scripts. Eg:
wget https://raw.githubusercontent.com/brendangregg/perf-tools/master/iosnoop
This preserves tabs (which copy-n-paste can mess up).
Warnings
Ftrace was first added to Linux 2.6.27, and perf_events to Linux 2.6.31. These early versions had kernel bugs, and lockups and panics have been reported on 2.6.32 series kernels. This includes CentOS 6.x. If you must analyze older kernels, these tools may only be useful in a fault-tolerant environment, such as a lab with simulated issues. These tools have been primarily developed on Linux 3.2 and later kernels.
Depending on the tool, there may also be overhead incurred. See the next section.
Internals and Overhead
perf_events is evolving. This collection began development circa Linux 3.16, with Linux 3.2 servers as the main target, at a time when perf_events lacks certain programmatic capabilities (eg, custom in-kernel aggregations). It's possible these will be added in a forthcoming kernel release. Until then, many of these tools employ workarounds, tricks, and hacks in order to work. Some of these tools pass event data to user space for post-processing, which costs much higher overhead than in-kernel aggregations. The overhead of each tool is described in its man page.
WARNING: In extreme cases, your target application may run 5x slower when using these tools. Depending on the tool and kernel version, there may also be the risk of kernel panics. Read the program header for warnings, and test before use.
If the overhead is a problem, these tools can be improved. If a tool doesn't already, it could be rewritten in C to use perf_events_open() and mmap() for the trace buffer. It could also implement frequency counts in C, and operate on mmap() directly, rather than using awk/Perl/Python. Additional improvements are possible for ftrace-based tools, such as use of snapshots and per-instance buffers.
Some of these tools are intended as short-term workarounds until more kernel capabilities exist, at which point they can be substantially rewritten. Older versions of these tools will be kept in this repository, for older kernel versions.
As my main target is a fleet of Linux 3.2 servers that do not have debuginfo, these tools try not to require it. At times, this makes the tool more brittle than it needs to be, as I'm employing workarounds (that may be kernel version and platform specific) instead of using debuginfo information (which can be generic). See the man page for detailed prerequisites for each tool.
I've tried to use perf_events ("perf") where possible, since that interface has been developed for multi-user use. For various reasons I've often needed to use ftrace instead. ftrace is surprisingly powerful (thanks Steven Rostedt!), and not all of its features are exposed via perf, or in common usage. This tool collection is in some ways a demonstration of hidden Linux features using ftrace.
Since things are changing, it's very possible you may find some tools don't work on your Linux kernel version. Some expertise and assembly will be required to fix them.
Links
A case study and summary:
Related articles:
一套使用 ftrace 和 perf_events（即 'perf' 命令）分析 Linux 性能的命令行脚本，由 Brendan Gregg（DTraceToolkit 作者）创建。