Chapter 13. Recording and analyzing performance profiles with perf

• Without root access: perf record collects data only in the user space.
• With root access: perf record collects data in both the user and kernel space.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.
• You have root access if you want to collect data for user and kernel space.

Procedure

• Do one of the following:

  • To sample and record the performance data for the user space:

    $ perf record command

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  • To sample and record the performance data for kernel space (use root or sudo access):

    # perf record command

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    Replace command with the actual command you want to profile. If you do not specify a command, then perf record samples data until you manually stop it by pressing Ctrl+C.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.

Procedure

• Sample and record the performance data:

  # perf record -a command

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  Replace command with the command you want to sample data during. If you do not specify a command, then perf record samples data until you manually stop it by pressing Ctrl+C.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.

Procedure

• Sample and record performance data with the --call-graph option:

  $ perf record --call-graph method command

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  • Replace command with the command you want to sample data during. If you do not specify a command, then perf record samples data until you manually stop it by pressing Ctrl+C.

  • Replace method with one of the following unwinding methods:

    fp

    Uses the frame pointer method. Depending on compiler optimization, such as with binaries built with the GCC option --fomit-frame-pointer, this may not be able to unwind the stack.

    dwarf

    Uses DWARF Call Frame Information to unwind the stack.

    lbr

    Uses the last branch record hardware on Intel processors.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.
• There is a perf.data file in the current directory.
• If the perf.data file was created with root access, you need to run perf report with root access too.

Procedure

• Display the contents of the perf.data file for further analysis:

  # perf report
  This command displays output similar to the following:
  Samples: 2K of event 'cycles', Event count (approx.): 235462960
  Overhead  Command          Shared Object                     Symbol
     2.36%  kswapd0          [kernel.kallsyms]                 [k] page_vma_mapped_walk
     2.13%  sssd_kcm         libc-2.28.so                      [.] memset_avx2_erms 2.13% perf [kernel.kallsyms] [k] smp_call_function_single 1.53% gnome-shell libc-2.28.so [.] strcmp_avx2
     1.17%  gnome-shell      libglib-2.0.so.0.5600.4           [.] g_hash_table_lookup
     0.93%  Xorg             libc-2.28.so                      [.] memmove_avx_unaligned_erms 0.89% gnome-shell libgobject-2.0.so.0.5600.4 [.] g_object_unref 0.87% kswapd0 [kernel.kallsyms] [k] page_referenced_one 0.86% gnome-shell libc-2.28.so [.] memmove_avx_unaligned_erms
     0.83%  Xorg             [kernel.kallsyms]                 [k] alloc_vmap_area
     0.63%  gnome-shell      libglib-2.0.so.0.5600.4           [.] g_slice_alloc
     0.53%  gnome-shell      libgirepository-1.0.so.1.0.0      [.] g_base_info_unref
     0.53%  gnome-shell      ld-2.28.so                        [.] _dl_find_dso_for_object
     0.49%  kswapd0          [kernel.kallsyms]                 [k] vma_interval_tree_iter_next
  0.48%  gnome-shell      libpthread-2.28.so                [.] pthread_getspecific 0.47% gnome-shell libgirepository-1.0.so.1.0.0 [.] 0x0000000000013b1d 0.45% gnome-shell libglib-2.0.so.0.5600.4 [.] g_slice_free1 0.45% gnome-shell libgobject-2.0.so.0.5600.4 [.] g_type_check_instance_is_fundamentally_a 0.44% gnome-shell libc-2.28.so [.] malloc 0.41% swapper [kernel.kallsyms] [k] apic_timer_interrupt 0.40% gnome-shell ld-2.28.so [.] _dl_lookup_symbol_x 0.39% kswapd0 [kernel.kallsyms] [k] raw_callee_save___pv_queued_spin_unlock

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  For more information, see the perf-record(1) man page on your system.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.

Procedure

• Attach perf record to a running process:

  $ perf record -p ID1,ID2 sleep seconds

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  This command samples and records performance data of the processes with the process ID’s ID1 and ID2 for a time period of seconds seconds as dictated by using the sleep command. You can also configure perf to record events in specific threads:

  $ perf record -t ID1,ID2 sleep seconds

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  Note

  When using the -t flag and stipulating thread ID’s, perf disables inheritance by default. You can enable inheritance by adding the --inherit option.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.
• The kernel debuginfo package is installed. For more information, see Getting debuginfo packages for an application or library using GDB.

Verification

• Verify that the archive file has been generated in your current active directory:

  # ls perf.data*

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  The output will display every file in your current directory that begins with perf.data. The archive file will be named either: perf.data.tar.gz or perf.data.tar.bz2.

Prerequisites

• You have the perf user space tool installed. For more information, see Installing perf.
• A perf.data file and associated archive file generated on a different device are present on the current device being used.