Re: Antw: [EXT] Re: [systemd‑devel] device unit files

["Ulrich Windl" <Ulrich.Windl@xxxxxxxxxxxxxxxxxxxx>]

>>> Lennart Poettering <lennart@xxxxxxxxxxxxxx> schrieb am 14.04.2022 um 09:45
in
Nachricht <YlfRAAL1mZDetjSS@gardel-login>:
> On Do, 14.04.22 08:00, Ulrich Windl (Ulrich.Windl@xxxxxx‑regensburg.de)
wrote:
> 
>> >>> Lennart Poettering <lennart@xxxxxxxxxxxxxx> schrieb am 13.04.2022 um
17:38
>> in
>> Nachricht <YlbufcsF05NFQiUt@gardel‑login>:
>> > On Di, 12.04.22 14:38, Elbek Mamajonov (emm.boxinuse@xxxxxxxxx) wrote:
>> >
>> >> On graph I have mmcblk.device taking 1.624s. From the point that
>> >> this partition is where my rootfs lies, and systems does remounting
>> >> of rootfs, I did look up for systemd‑remount‑fs.service, it took
>> >> 231ms, and systemd‑udev‑trigger.service, as you suggested, it took
>> >> 517ms to become active. But even after systemd‑udev‑trigger.service
>> >> becomes active there is about 800ms for mmcblk.device to become
>> >> active. Are those services related to the activation of the
>> >> mmcblk.device? Can I consider those 231ms and 517ms as a part of the
>> >> activation time of the mmcblk.device? How can I debug udev in this
>> >> case?
>> >
>> > "systemd‑udev‑trigger.service" might take a while before it completes,
>> > since it triggers basically all devices in the system.
>> >
>> > It might be worth triggering block devices first. With upcoming v251
>>
>> What is the expected benefit? On bigger servers with hundreds of disks
this
>> may take longest.
> 
> There are a myriad of devices on current systems. Traditionally, we
> trigger them at boot in alphabetical order by their sysfs path (more
> or less that is). Only once triggered subsystems waiting for them will
> see the devices. Since at boot typically the most waited for devices
> are block devices it's thus benefical to trigger them first, as this
> unblocks a major part of the rest of the boot process.
> 
> Or in other words: nothing really "waits" for your mouse to show up in
> the device table. Everyting waits for your root block device to show
> up. Hence trigger the root block device first, and the mouse later.

Hi!

I agree, but (how) can you trigger only the root block device?
Apr 01 08:46:25 h16 kernel: sd 0:2:0:0: [sda] 467664896 512-byte logical
blocks: (239 GB/223 GiB)
...
Apr 01 08:46:33 h16 kernel: sd 3:0:7:2: [sdda] 524288 512-byte logical blocks:
(268 MB/256 MiB)
...
That's 8 seconds to discover the devices

Apr 01 08:47:04 h16 kernel: sd 2:0:5:2: alua: port group 01 state A preferred
supports tolusnA

And another 30 seconds until multipath has settled.

Apr 01 08:47:04 h16 systemd[1]: Reached target System Initialization.

Regards,
Ulrich

> 
> Lennart
> 
> ‑‑
> Lennart Poettering, Berlin