I spent some time doing some research on a USB drive caching error that pops up. The supposed solution is to enter usb_storage in /etc/modules.
That didn't work to get rid of the issue, but it got me to thinking... during boot, the machine has to scan all the hardware, then scan through a huge set of potential kernel modules to load...
modprobe -c | wc -l
47415
... although the majority of that are aliases.
If you do:
modprobe -c | awk -F ' ' '{print $3}' | sort | uniq | wc -l
5314
You can list them all via:
modprobe -c | awk -F ' ' '{print $3}' | sort | uniq
... what if all those kernel modules used were already loaded?
So I issued:
lsmod
That gave me all the kernel modules being loaded. I figured it'd speed things up if they were loaded by order of when they were used, and since it's not really possible to find that information, I used the module dependencies and the general loading order during boot.
So I had a long list:
Summary
Module Size Used by
rfcomm 81920 4
bnep 28672 2
sch_fq_codel 24576 1
cmac 16384 6
ccm 20480 6
algif_skcipher 16384 3
algif_hash 16384 3
af_alg 32768 14 algif_hash,algif_skcipher
snd_hda_codec_realtek 155648 1
snd_hda_codec_hdmi 77824 1
snd_hda_codec_generic 102400 1 snd_hda_codec_realtek
snd_ctl_led 24576 0
ledtrig_audio 16384 2 snd_ctl_led,snd_hda_codec_generic
snd_acp3x_rn 16384 2
snd_soc_dmic 16384 1
snd_acp3x_pdm_dma 16384 1
snd_soc_core 335872 3 snd_acp3x_rn,snd_soc_dmic,snd_acp3x_pdm_dma
snd_hda_intel 53248 8
snd_usb_audio 356352 3
snd_intel_dspcfg 28672 1 snd_hda_intel
rtw88_8822ce 16384 0
snd_intel_sdw_acpi 20480 1 snd_intel_dspcfg
rtw88_8822c 503808 1 rtw88_8822ce
snd_compress 24576 1 snd_soc_core
snd_hda_codec 163840 4 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec_realtek
uvcvideo 106496 0
ac97_bus 16384 1 snd_soc_core
snd_pcm_dmaengine 16384 1 snd_soc_core
crct10dif_pclmul 16384 1
ghash_clmulni_intel 16384 0
snd_usbmidi_lib 45056 1 snd_usb_audio
snd_hda_core 110592 5 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec,snd_hda_codec_realtek
aesni_intel 376832 13
snd_hwdep 16384 2 snd_usb_audio,snd_hda_codec
btusb 61440 0
btrtl 24576 1 btusb
snd_pci_acp6x 16384 0
rtw88_pci 32768 1 rtw88_8822ce
snd_pcm 135168 14 snd_hda_codec_hdmi,snd_pci_acp6x,snd_hda_intel,snd_usb_audio,snd_hda_codec,snd_compress,snd_soc_core,snd_hda_core,snd_acp3x_pdm_dma,snd_pcm_dmaengine
snd_seq_midi 20480 0
videobuf2_vmalloc 20480 1 uvcvideo
rtw88_core 262144 2 rtw88_pci,rtw88_8822c
snd_seq_midi_event 16384 1 snd_seq_midi
btbcm 24576 1 btusb
videobuf2_memops 20480 1 videobuf2_vmalloc
videobuf2_v4l2 32768 1 uvcvideo
snd_rawmidi 45056 2 snd_seq_midi,snd_usbmidi_lib
videobuf2_common 77824 4 videobuf2_vmalloc,videobuf2_v4l2,uvcvideo,videobuf2_memops
btintel 40960 1 btusb
bluetooth 696320 31 btrtl,btintel,btbcm,bnep,btusb,rfcomm
snd_seq 73728 2 snd_seq_midi,snd_seq_midi_event
mac80211 1261568 2 rtw88_pci,rtw88_core
crypto_simd 16384 1 aesni_intel
cryptd 24576 5 crypto_simd,ghash_clmulni_intel
binfmt_misc 24576 1
exfat 86016 1
ecdh_generic 16384 1 bluetooth
snd_seq_device 16384 3 snd_seq,snd_seq_midi,snd_rawmidi
input_leds 16384 0
videodev 253952 3 videobuf2_v4l2,uvcvideo,videobuf2_common
serio_raw 20480 0
snd_timer 40960 2 snd_seq,snd_pcm
nls_iso8859_1 16384 2
mc 61440 5 videodev,snd_usb_audio,videobuf2_v4l2,uvcvideo,videobuf2_common
joydev 28672 0
cfg80211 978944 2 rtw88_core,mac80211
snd 102400 38 snd_ctl_led,snd_hda_codec_generic,snd_seq,snd_seq_device,snd_hda_codec_hdmi,snd_hwdep,snd_hda_intel,snd_usb_audio,snd_usbmidi_lib,snd_hda_codec,snd_hda_codec_realtek,snd_timer,snd_compress,snd_soc_core,snd_pcm,snd_rawmidi
ecc 36864 1 ecdh_generic
soundcore 16384 2 snd_ctl_led,snd
snd_pci_acp5x 20480 0
snd_rn_pci_acp3x 20480 0
snd_pci_acp3x 20480 0
libarc4 16384 1 mac80211
hid_multitouch 32768 0
mac_hid 16384 0
xt_hl 16384 22
ip6t_rt 20480 3
ip6t_REJECT 16384 3
hp_wmi 20480 0
nf_reject_ipv6 20480 1 ip6t_REJECT
wmi_bmof 16384 0
platform_profile 16384 1 hp_wmi
sparse_keymap 16384 1 hp_wmi
xt_limit 16384 1
xt_addrtype 16384 4
acpi_tad 16384 0
xt_tcpudp 20480 20
xt_conntrack 16384 14
nf_conntrack 172032 1 xt_conntrack
nf_defrag_ipv6 24576 1 nf_conntrack
nf_defrag_ipv4 16384 1 nf_conntrack
edac_mce_amd 36864 0
libcrc32c 16384 1 nf_conntrack
kvm_amd 155648 0
kvm 1015808 1 kvm_amd
ipt_REJECT 16384 3
nf_reject_ipv4 16384 1 ipt_REJECT
ccp 102400 1 kvm_amd
ip6table_filter 16384 1
k10temp 16384 0
ip6_tables 32768 53 ip6table_filter
rapl 20480 0
iptable_filter 16384 1
intel_rapl_msr 20480 0
bpfilter 16384 0
intel_rapl_common 40960 1 intel_rapl_msr
msr 16384 0
ramoops 28672 0
reed_solomon 28672 1 ramoops
pstore_blk 16384 0
pstore_zone 32768 1 pstore_blk
efi_pstore 16384 0
ip_tables 32768 9 iptable_filter
x_tables 53248 12 ip6table_filter,xt_conntrack,iptable_filter,xt_tcpudp,xt_addrtype,ip6t_rt,ip6_tables,ipt_REJECT,ip_tables,xt_limit,xt_hl,ip6t_REJECT
autofs4 45056 2
zfs 3821568 23
zunicode 348160 1 zfs
zzstd 487424 1 zfs
zlua 163840 1 zfs
zavl 20480 1 zfs
icp 323584 1 zfs
zcommon 106496 2 zfs,icp
znvpair 98304 2 zfs,zcommon
spl 122880 6 zfs,icp,zzstd,znvpair,zcommon,zavl
ses 20480 0
enclosure 16384 1 ses
scsi_transport_sas 45056 1 ses
usbhid 65536 0
uas 28672 3
usb_storage 77824 10 uas
amdgpu 9814016 21
iommu_v2 24576 1 amdgpu
gpu_sched 45056 1 amdgpu
i2c_algo_bit 16384 1 amdgpu
drm_ttm_helper 16384 1 amdgpu
ttm 86016 2 amdgpu,drm_ttm_helper
drm_kms_helper 307200 1 amdgpu
syscopyarea 16384 1 drm_kms_helper
sysfillrect 20480 1 drm_kms_helper
sysimgblt 16384 1 drm_kms_helper
fb_sys_fops 16384 1 drm_kms_helper
cec 77824 1 drm_kms_helper
hid_generic 16384 0
ahci 45056 4
xhci_pci 24576 0
i2c_hid_acpi 16384 0
rc_core 61440 1 cec
crc32_pclmul 16384 0
i2c_hid 36864 1 i2c_hid_acpi
drm 614400 13 gpu_sched,drm_kms_helper,amdgpu,drm_ttm_helper,ttm
i2c_piix4 28672 0
libahci 45056 1 ahci
xhci_pci_renesas 20480 1 xhci_pci
wmi 32768 2 hp_wmi,wmi_bmof
video 57344 0
hid 147456 4 i2c_hid,usbhid,hid_multitouch,hid_generic
So what I did is to take one of those above that have a "Used by" in the right-hand column, then search for all those dependencies.
So, for instance:
ecc 36864 1 ecdh_generic
ecdh_generic 16384 1 bluetooth
bluetooth 696320 31 btrtl,btintel,btbcm,bnep,btusb,rfcomm
btrtl 24576 1 btusb
btintel 40960 1 btusb
btbcm 24576 1 btusb
bnep 28672 2
btusb 61440 0
rfcomm 81920 4
I did that for each category (UEFI, CPU, memory, GPU, crypto, USB, storage, network, WiFi, Bluetooth, etc.), and arranged each category in the order that the system checks things.
Then I simply stripped off the extraneous information. For instance:
ecc
ecdh_generic
bluetooth
btrtl
btintel
btbcm
bnep
btusb
rfcomm
There were some modules I didn't know which category to put into. I used modinfo and web searches to figure out what those modules did. So, for instance:
modinfo btusb
description: Generic Bluetooth USB driver ver 0.8
Once that was all done, I created a manual ZFS snapshot (so I could roll back if what I was doing borked things), then saved /etc/modules with the long list of modules to pre-load, then rebooted.
The result? The total load time to Run Level 5 (the desktop) was reduced by ~1 second... the kernel time to load the modules was front-loaded and all-at-once and it took 10.656s, but once the modules were loaded, it was at the desktop in only 6.785s.
If I could figure out some way of moving all the boot files to the fastest part of the disk and locking them there (so they can't be moved), it'd probably shave another second off that time. They'd be loaded without the drive having to seek much.
This would likely have a far greater effect on a machine with a SSD... the modules would pre-load without any seek time, so the boot would be somewhere around 8 seconds total on this machine.