NAME

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

SYNOPSIS

       profile [-adfh] [-p PID] [-U | -k] [-F FREQUENCY] [--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 (default 49).

       -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
              10240). If the sampled count exceeds this, a warning will be printed.

       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 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)