On Fri, 7 Oct 2022 15:30:56 +0200 Paul Menzel <pmenzel@xxxxxxxxxxxxx> wrote: > 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? "function" tracing is enabled by then (I just tested it), but "function_graph" is not. Function graph requires trace events enabled, but I could see what happens if I do enabled it ;-) > > Is there another way to trace the serial console init, without having to > add print statements? > Use "ftrace=function" but then you will get everything. You could add a "set_filter=<func>:traceoff" to set a trigger that would disable tracing, if you can find a function that would be good to stop tracing with. Otherwise, I could take a look to see what it takes to get function graph tracing working that early. -- Steve
