Initcall Debug

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Passing the initcall_debug option on the kernel command line will cause timing information to be printed to the console for each initcall. initcalls are used to initialize statically linked kernel drivers and subsystems and contribute a significant amount of time to the Linux boot process. The output looks like this:

calling ipc_init+0x0/0x28 @ 1
msgmni has been set to 42
initcall ipc_init+0x0/0x28 returned 0 after 1872 usecs

You can use 'dmesg' to see the messages after the kernel has booted. With a sort 'sed' script, you can reorder the final 'timing' line, and short the initcalls numerically by duration. Here is a command to do this:

dmesg -s 128000 | grep "initcall" | sed "s/(.*\)after\(.*\)/\2 \1/g" | sort -n

Sample output

Here is some sample output from the above command sequence. This was on an old X86-based desktop system. Printk Times was turned on (hence the extra timestamp on each line.)

24 msecs [ 2.237177] initcall acpi_button_init+0x0/0x51 returned 0
28 msecs [ 0.763503] initcall init_acpi_pm_clocksource+0x0/0x16c returned 0
32 msecs [ 0.348241] initcall acpi_pci_link_init+0x0/0x43 returned 0
33 msecs [ 0.919004] initcall inet_init+0x0/0x1c7 returned 0
33 msecs [ 5.282722] initcall psmouse_init+0x0/0x5e returned 0
54 msecs [ 2.979825] initcall e100_init_module+0x0/0x4d returned 0
71 msecs [ 0.650325] initcall pnp_system_init+0x0/0xf returned 0
91 msecs [ 0.872402] initcall pcibios_assign_resources+0x0/0x85 returned 0
187 msecs [ 4.369187] initcall ehci_hcd_init+0x0/0x70 returned 0
245 msecs [ 2.777161] initcall serial8250_init+0x0/0x100 returned 0
673 msecs [ 5.098052] initcall uhci_hcd_init+0x0/0xc1 returned 0
830 msecs [ 4.067279] initcall piix_init+0x0/0x27 returned 0
1490 msecs [ 8.290606] initcall ip_auto_config+0x0/0xd70 returned 0


Using initcall_debug increases the amount of messages produced by the kernel during system boot. It's a good idea to increase the printk log buffer size to avoid overflowing the log buffer. To do this, increase the value of CONFIG_lOGBUF_SHIFT from 14 to 18. This increases the log buffer from the default size of 16k to 256K.