Provided by: bpfcc-tools_0.8.0-4_all bug

NAME

       profile - Profile CPU usage by sampling stack traces. Uses Linux eBPF/bcc.

SYNOPSIS

       profile  [-adfh] [-p PID] [-U | -K] [-F FREQUENCY | -c COUNT] [--stack-storage-size COUNT]
       [duration]

DESCRIPTION

       This is a CPU profiler. It works by taking samples of stack traces at timed intervals.  It
       will help you understand and quantify CPU usage: which code is executing, and by how much,
       including both user-level and kernel code.

       By default this samples at 49 Hertz (samples per second), across all CPUs.  This frequency
       can be tuned using a command line option. The reason for 49, and not 50, is to avoid lock-
       step sampling.

       This is also an efficient profiler, as  stack  traces  are  frequency  counted  in  kernel
       context,  rather  than passing each stack to user space for frequency counting there. Only
       the unique stacks and counts are passed to user space at the end of the  profile,  greatly
       reducing the kernel<->user transfer.

REQUIREMENTS

       CONFIG_BPF and bcc.

       This  also  requires  Linux  4.9+ (BPF_PROG_TYPE_PERF_EVENT support). See tools/old for an
       older version that may work on Linux 4.6 - 4.8.

OPTIONS

       -h     Print usage message.

       -p PID Trace this process ID  only  (filtered  in-kernel).  Without  this,  all  CPUs  are
              profiled.

       -F frequency
              Frequency to sample stacks.

       -c count
              Sample stacks every one in this many events.

       -f     Print output in folded stack format.

       -d     Include  an  output  delimiter  between kernel and user stacks (either "--", or, in
              folded mode, "-").

       -U     Show stacks from user space only (no kernel space stacks).

       -K     Show stacks from kernel space only (no user space stacks).

       --stack-storage-size COUNT
              The maximum number of unique stack traces  that  the  kernel  will  count  (default
              16384). If the sampled count exceeds this, a warning will be printed.

       -C cpu Collect stacks only from specified cpu.

       duration
              Duration to trace, in seconds.

EXAMPLES

       Profile (sample) stack traces system-wide at 49 Hertz (samples per second) until Ctrl-C:
              # profile

       Profile for 5 seconds only:
              # profile 5

       Profile at 99 Hertz for 5 seconds only:
              # profile -F 99 5

       Profile 1 in a million events for 5 seconds only:
              # profile -c 1000000 5

       Profile PID 181 only:
              # profile -p 181

       Profile  for  5  seconds  and  output  in folded stack format (suitable as input for flame
       graphs), including a delimiter between kernel and user stacks:
              # profile -df 5

       Profile kernel stacks only:
              # profile -K

DEBUGGING

       See "[unknown]" frames with bogus addresses? This can happen for different  reasons.  Your
       best  approach  is  to  get Linux perf to work first, and then to try this tool. Eg, "perf
       record -F 49 -a -g -- sleep 1; perf script", and to check for unknown frames there.

       The most common reason for "[unknown]" frames is that the target  software  has  not  been
       compiled  with  frame  pointers,  and  so  we can't use that simple method for walking the
       stack. The fix in that case is to use software that does  have  frame  pointers,  eg,  gcc
       -fno-omit-frame-pointer, or Java's -XX:+PreserveFramePointer.

       Another  reason  for  "[unknown]"  frames  is JIT compilers, which don't use a traditional
       symbol table. The fix in that case is  to  populate  a  /tmp/perf-PID.map  file  with  the
       symbols,  which  this  tool  should  read.  How  you do this depends on the runtime (Java,
       Node.js).

       If you seem to have unrelated samples in the output, check for other sampling  or  tracing
       tools  that  may  be running. The current version of this tool can include their events if
       profiling happened concurrently. Those samples may be filtered in a future version.

OVERHEAD

       This is an efficient profiler, as stack traces are frequency counted  in  kernel  context,
       and  only  the unique stacks and their counts are passed to user space. Contrast this with
       the current "perf record -F 99 -a" method of profiling, which writes each sample  to  user
       space  (via  a  ring buffer), and then to the file system (perf.data), which must be post-
       processed.

       This uses perf_event_open to  setup  a  timer  which  is  instrumented  by  BPF,  and  for
       efficiency  it does not initialize the perf ring buffer, so the redundant perf samples are
       not collected.

       It's expected that the overhead while sampling at 49 Hertz (the default), across all CPUs,
       should  be  negligible.  If  you  increase the sample rate, the overhead might begin to be
       measurable.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also look in the bcc distribution for a companion _examples.txt  file  containing  example
       usage, output, and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       offcputime(8)