CONFIG_FTRACE=y significantly slowing down module loading

[Hans de Goede <hans@hansg.org>]

Hi Everyone,

On some old hw CONFIG_FTRACE=y causes "modprobe amdgpu" to take
25-30 seconds, halting the entire boot process for that time.
Where as with "# CONFIG_FTRACE is not set" this takes only 2 seconds.

I believe this was reported before by Mario (in the Cc) and there was
a fix of sorts merged for 6.15? But there still is a significant
slowdown (especially on slow hardware).

I was also the reason Mario originally reported this and Mario
asked me to test 6.15 but I was busy with other stuff so from
the better late then never department I only got around this now...

I've tested this on 2 admittedly quite old and slow machines,
but the impact is big enough that fixing this might also help
speeding up modprobe on modern machines.

This was tested on:

MSI S270 laptop, AMD Turion 64 MT-30 CPU, RS480 iGPU
FUJITSU D3003-S2 industrial PC, AMD G-T56N CPU, Radeon HD 6320 iGPU

Both old machines where amdgpu.ko auto-loads.

Kernel/modprobe real-/sys-time/FTRACE Kconfig enabled/machine
6.19.6		32.5s/31.8s	yes	MSI S270
7.0.0		25.5s/22.8s	yes	FUJITSU D3003-S2
6.15-rc7	27.7s/26.5s	yes	FUJITSU D3003-S2
7.0.0		1.9s/1.1s	no	FUJITSU D3003-S2

Regards,

Hans