FWIW, none of the usual pi overclocking setting make any difference in boot time…
I’ve tried the following settings in /DietPi/config.txt
temp_limit=65
initial_turbo=30
arm_freq=1000
gpu_freq=500
core_freq=500
sdram_freq=500
sdram_schmoo=0x02000020
over_voltage=2
sdram_over_voltage=2
And whether they are all commented or all uncommitted, I get identical boot time of ~25 sec (per /var/log/boottime) with dmesg ending as follows…
[ 3.486860] systemd[1]: Listening on Journal Socket.
[ 3.493561] systemd[1]: Starting System Slice.
[ 3.507882] systemd[1]: Created slice System Slice.
[ 3.514644] systemd[1]: Starting File System Check on Root Device...
[ 3.534336] systemd[1]: Starting system-systemd\x2dfsck.slice.
[ 3.560703] systemd[1]: Created slice system-systemd\x2dfsck.slice.
[ 3.571560] systemd[1]: Starting system-getty.slice.
[ 3.596157] systemd[1]: Created slice system-getty.slice.
[ 3.603989] systemd[1]: Starting Nameserver information manager...
[ 3.635376] systemd[1]: Mounting POSIX Message Queue File System...
[ 3.678156] systemd[1]: Mounted Huge Pages File System.
[ 3.715903] systemd[1]: Mounting Debug File System...
[ 3.750469] systemd[1]: Starting Create list of required static device nodes for the current kernel...
[ 3.913660] systemd[1]: Started Set Up Additional Binary Formats.
[ 3.940740] systemd[1]: Starting Load Kernel Modules...
[ 3.987038] systemd[1]: Starting udev Coldplug all Devices...
[ 4.067408] systemd[1]: Starting LSB: Set keymap...
[ 4.133578] fuse init (API version 7.23)
[ 4.153447] systemd[1]: Starting Journal Service...
[ 4.229576] systemd[1]: Started Journal Service.
[ 4.278682] bcm2708_i2c 20804000.i2c: BSC1 Controller at 0x20804000 (irq 77) (baudrate 100000)
[ 4.319622] i2c /dev entries driver
[ 6.054366] systemd-udevd[135]: starting version 215
[ 7.526692] rtc-pcf8523 1-0068: rtc core: registered rtc-pcf8523 as rtc0
[ 7.693995] bcm2835-wdt 20100000.watchdog: Broadcom BCM2835 watchdog timer
[ 7.741191] gpiomem-bcm2835 20200000.gpiomem: Initialised: Registers at 0x20200000
[ 8.126068] EXT4-fs (mmcblk0p2): re-mounted. Opts: discard
[ 9.334761] usbcore: registered new interface driver brcmfmac
[ 9.547133] brcmfmac: brcmf_c_preinit_dcmds: Firmware version = wl0: May 27 2016 00:13:38 version 7.45.41.26 (r640327) FWID 01-df77e4a7
[ 9.571770] random: nonblocking pool is initialized
[ 9.596586] brcmfmac: brcmf_cfg80211_reg_notifier: not a ISO3166 code
[ 10.393194] systemd-journald[97]: Received request to flush runtime journal from PID 1
[ 12.258605] brcmfmac: brcmf_cfg80211_reg_notifier: not a ISO3166 code
[ 12.258661] cfg80211: World regulatory domain updated:
[ 12.258678] cfg80211: DFS Master region: unset
[ 12.258694] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp), (dfs_cac_time)
[ 12.258715] cfg80211: (2402000 KHz - 2472000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)
[ 12.258737] cfg80211: (2457000 KHz - 2482000 KHz @ 20000 KHz, 92000 KHz AUTO), (N/A, 2000 mBm), (N/A)
[ 12.258753] cfg80211: (2474000 KHz - 2494000 KHz @ 20000 KHz), (N/A, 2000 mBm), (N/A)
[ 12.258774] cfg80211: (5170000 KHz - 5250000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (N/A)
[ 12.258793] cfg80211: (5250000 KHz - 5330000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (0 s)
[ 12.258810] cfg80211: (5490000 KHz - 5730000 KHz @ 160000 KHz), (N/A, 2000 mBm), (0 s)
[ 12.258826] cfg80211: (5735000 KHz - 5835000 KHz @ 80000 KHz), (N/A, 2000 mBm), (N/A)
[ 12.258842] cfg80211: (57240000 KHz - 63720000 KHz @ 2160000 KHz), (N/A, 0 mBm), (N/A)
[ 12.917421] cfg80211: Regulatory domain changed to country: US
[ 12.917465] cfg80211: DFS Master region: FCC
[ 12.917483] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp), (dfs_cac_time)
[ 12.917507] cfg80211: (2402000 KHz - 2472000 KHz @ 40000 KHz), (N/A, 3000 mBm), (N/A)
[ 12.917529] cfg80211: (5170000 KHz - 5250000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2300 mBm), (N/A)
[ 12.917549] cfg80211: (5250000 KHz - 5330000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2300 mBm), (0 s)
[ 12.917567] cfg80211: (5490000 KHz - 5730000 KHz @ 160000 KHz), (N/A, 2300 mBm), (0 s)
[ 12.917583] cfg80211: (5735000 KHz - 5835000 KHz @ 80000 KHz), (N/A, 3000 mBm), (N/A)
[ 12.917600] cfg80211: (57240000 KHz - 63720000 KHz @ 2160000 KHz), (N/A, 4000 mBm), (N/A)
[ 13.769960] brcmfmac: brcmf_add_if: ERROR: netdev:wlan0 already exists
[ 13.770003] brcmfmac: brcmf_add_if: ignore IF event
[ 13.780044] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 13.780124] brcmfmac: power management disabled
[ 14.093267] brcmfmac: power management disabled
[ 16.278037] Adding 102396k swap on /var/swap. Priority:-1 extents:3 across:106492k SSFS
[ 17.869005] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
[ 34.407252] brcmfmac: power management disabled