Re: ftrace: function radeon_init not traceable

Paul Menzel Mon, 11 May 2020 16:08:02 -0700

Dear Steven,


Thank you for your quick response.

Am 11.05.20 um 20:58 schrieb Steven Rostedt:

On Sat, 9 May 2020 12:16:30 +0200 Paul Menzel wrote:

Linux master and Linux 5.6.7 (from Debian Sid/unstable) are used.

Instrumenting Linux’ start-up time, I’d like to trace the init function
of the Radeon graphics driver `radeon_init()` (built as a module).

      drivers/gpu/drm/radeon/radeon_drv.c:static int __init radeon_init(void)
      drivers/gpu/drm/radeon/radeon_drv.c:module_init(radeon_init);

With `initcall_debug` I can see:

      [    1.079920] calling  radeon_init+0x0/0x1000 [radeon] @ 138
      [    1.663200] initcall radeon_init+0x0/0x1000 [radeon] returned 0
after 129346 usecs

With `function_graph` as the trace, I am adding the string below to the
Linux kernel CLI.

      initcall_debug log_buf_len=32M trace_buf_size=57074K trace_clock=global 
trace_options=nooverwrite,funcgraph-abstime,funcgraph-cpu,funcgraph-duration,funcgraph-proc,funcgraph-tail,nofuncgraph-overhead,context-info,graph-time
 ftrace=function_graph ftrace_graph_max_depth=1 ftrace_graph_filter=radeon_init

But ftrace “rejects” that:

      [    0.075538] ftrace: allocating 30958 entries in 61 pages
      [    0.084542] ftrace: allocated 61 pages with 5 groups
      [    0.094184] ftrace: function radeon_init not traceable

I believe it worked in the past. Is there a way to trace that init function?


Did it every work for modules? radeon_init() isn't in the symbol table at
boot up.

[   15.066951] systemd-journald[124]: Successfully sent stream file descriptor 
to service manager.
[   15.098265] hub 1-0:1.0: USB hub found
[   15.104006] systemd-journald[124]: Successfully sent stream file descriptor 
to service manager.
[   15.112965] hub 1-0:1.0: 2 ports detected
[   15.118116] probe of 1-0:1.0 returned 1 after 19873 usecs
[   15.124007] calling  radeon_init+0x0/0x1000 [radeon] @ 133

The radeon_init is called after systemd is running, so it is definitely
from a module.

Perhaps you had it built in before?

You are right. Probably I did. Can you suggest how to set up ftrace totrace a module?

Despite the function not being traceable, the trace file is still
filled. I’d would have expected to be empty.

```
# tracer: function_graph
#
#     TIME        CPU  TASK/PID         DURATION FUNCTION CALLS
#      |          |     |    |           |   |                     |   |     |  
 |
      2.910887 |   0)    <idle>-0    |   2.662 us    |  local_touch_nmi();
      2.910888 |   0)    <idle>-0    |   0.497 us    |  local_touch_nmi();
      2.910888 |   0)    <idle>-0    |   0.346 us    |  local_touch_nmi();
      2.910888 |   1)   systemd-1    |   1.440 us    |  __text_poke();
      2.910888 |   1)   systemd-1    |   0.588 us    |  __text_poke();
      2.910888 |   1)   systemd-1    |   0.556 us    |  __text_poke();
      2.910888 |   1)   systemd-1    |   0.489 us    |  __text_poke();
[…]
      2.910889 |   1)   systemd-1    |   0.530 us    |  __text_poke();
      2.910889 |   0)    <idle>-0    |   0.473 us    |  do_sync_core();
      2.910889 |   1)   systemd-1    |   0.572 us    |  do_sync_core();
      2.910889 |   0)    <idle>-0    |   0.365 us    | arch_cpu_idle_enter();
      2.910889 |   1)   systemd-1    |   0.830 us    |  __text_poke();
      2.910889 |   0)    <idle>-0    | ! 278.143 us  |  arch_cpu_idle();
      2.910889 |   1)   systemd-1    |   0.582 us    |  __text_poke();
[…]
```


Probably because the filtering failed, so there is no filter.


Is that the intended behavior? Or should nothing be traced?


Kind regards,

Paul

Re: ftrace: function radeon_init not traceable

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