linux-kernel - `switch_ldt()` fills up trace file

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Message-ID: <fe5695d3-b645-08a4-848e-262e291aea76@molgen.mpg.de>
Date:   Tue, 13 Sep 2022 09:48:35 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: `switch_ldt()` fills up trace file

Dear Linux folks,


Using `bootgraph.py -f -manual` [1] to generate the Linux CLI line for 
tracing the boot, and changing `do_one_initcall` to `dell_init` to trace 
`drivers/platform/x86/dell/dell-laptop.c`, `switch_ldt();` fills up the 
trace file. Is that expected, and can I work around it?

```
# boot-091222-181507 dellxps139360 boot 5.19.0-1-amd64
# sysinfo | man:Dell Inc. | plat:XPS 13 9360 | cpu:Intel(R) Core(TM) 
i7-7500U CPU @ 2.70GHz | bios:2.21.0 | biosdate:06/02/2022 | numcpu:4 | 
memsz:15959616 | memfr:11084888 | os:Debian GNU/Linux bookworm/sid
# command | analyze_boot.py -f
# kparams | BOOT_IMAGE=/vmlinuz-5.19.0-1-amd64 
root=UUID=fe58fd63-a3e1-4670-b648-45c6a324394a ro initcall_debug 
log_buf_len=32M trace_buf_size=524288K 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=5 
ftrace_graph_filter=dell_init cryptomgr.notests
# tracer: function_graph
#
#     TIME        CPU  TASK/PID         DURATION 
FUNCTION CALLS
#      |          |     |    |           |   |                     |   | 
   |   |
     0.516713 |   0)   systemd-1    |   1.671 us    |  switch_ldt();
     0.516715 |   0)   systemd-1    |   0.207 us    |  switch_ldt();
     0.516716 |   0)   systemd-1    |   0.170 us    |  switch_ldt();
[…]
```


Kind regards,

Paul


[1]: https://github.com/intel/pm-graph