Dear Linux folks,
I am trying to do boot-time tracing of `univ8250_console_init()`:
[ 0.126636] ftrace: allocating 41793 entries in 164 pages
[ 0.132446] ftrace: allocated 164 pages with 3 groups
[…]
[ 0.167334] calling con_init+0x0/0x239 @ 0
[ 0.170217] Console: colour VGA+ 80x25
[ 0.190381] printk: console [tty0] enabled
[ 0.190484] initcall con_init+0x0/0x239 returned 0 after 0 usecs
[ 0.190487] calling hvc_console_init+0x0/0x18 @ 0
[ 0.190489] initcall hvc_console_init+0x0/0x18 returned 0 after
0 usecs
[ 0.190491] calling univ8250_console_init+0x0/0x2b @ 0
[ 1.488645] printk: console [ttyS0] enabled
[ 1.492945] initcall univ8250_console_init+0x0/0x2b returned 0
after 0 usecs
[…]
[ 1.670397] calling trace_init_perf_perm_irq_work_exit+0x0/0x17 @ 1
[ 1.670399] initcall trace_init_perf_perm_irq_work_exit+0x0/0x17
returned 0 after 0 usecs
[…]
[ 1.673339] calling trace_init_flags_sys_enter+0x0/0x13 @ 1
[ 1.673342] initcall trace_init_flags_sys_enter+0x0/0x13
returned 0 after 0 usecs
[ 1.673344] calling trace_init_flags_sys_exit+0x0/0x13 @ 1
[ 1.673346] initcall trace_init_flags_sys_exit+0x0/0x13 returned
0 after 0 usecs
[ 1.673348] calling cpu_stop_init+0x0/0x87 @ 1
[ 1.673364] initcall cpu_stop_init+0x0/0x87 returned 0 after 0 usecs
[ 1.673366] calling init_kprobes+0x0/0x149 @ 1
[ 1.673495] initcall init_kprobes+0x0/0x149 returned 0 after 0 usecs
[ 1.673497] calling init_events+0x0/0x4d @ 1
[ 1.673502] initcall init_events+0x0/0x4d returned 0 after 0 usecs
[ 1.673504] calling init_trace_printk+0x0/0xc @ 1
[ 1.673505] initcall init_trace_printk+0x0/0xc returned 0 after
0 usecs
[ 1.673507] calling event_trace_enable_again+0x0/0x23 @ 1
[ 1.673508] initcall event_trace_enable_again+0x0/0x23 returned
0 after 0 usecs
The function `univ8250_console_init()` is not available in
`/sys/kernel/debug/tracing/available_filter_functions`, so I’d like to
trace `univ8250_console_setup()`:
initcall_debug log_buf_len=32M trace_buf_size=262144K
trace_clock=global
trace_options=nooverwrite,funcgraph-abstime,funcgraph-cpu,funcgraph-duration,funcgraph-proc,funcgraph-tail,nofuncgraph-overhead,context-info,graph-time
ftrace=fun
ction_graph ftrace_graph_max_depth=2
ftrace_graph_filter=univ8250_console_setup tp_printk
Unfortunately, `/sys/kernel/debug/tracing/trace` is empty, so I guess
the console happens before ftrace is available?
Is there another way to trace the serial console init, without having to
add print statements?
Kind regards,
Paul
PS: We boot our systems generally with the serial console enabled
`console=ttyS0`, and noticed that initializing the console takes at
least one second.
$ dmesg | grep -e 'DMI:' -e 'printk: console'
[ 0.000000] DMI: Dell Inc. PowerEdge R7525/05Y13N, BIOS 2.7.3 03/30/2022
[ 2.691432] printk: console [tty0] enabled
[ 5.414384] printk: console [ttyS0] enabled
$ dmesg | grep -e 'DMI:' -e 'printk:'
[ 0.000000] DMI: Dell Inc. Precision Tower 3620/0MWYPT, BIOS 2.22.0
07/13/2022
[ 0.146953] printk: console [tty0] enabled
[ 1.374382] printk: console [ttyS0] enabled
$ dmesg | grep -e 'DMI:' -e 'printk: console'
[ 0.000000] DMI: Dell Inc. PowerEdge R7425/08V001, BIOS 1.6.7 10/29/2018
[ 1.589543] printk: console [tty0] enabled
[ 3.057770] printk: console [ttyS0] enabled
$ dmesg | grep -e 'DMI:' -e 'printk: console'
[ 0.000000] DMI: HPE ProLiant DL385 Gen10 Plus/ProLiant DL385 Gen10
Plus, BIOS A42 12/03/2021
[ 5.171202] printk: console [tty0] enabled
[ 8.066602] printk: console [ttyS0] enabled
