[systemd-devel] device units rely on udev rules?

[Koen Kooi]

Op 9 mei 2011, om 22:23 heeft Kay Sievers het volgende geschreven:

> On Mon, May 9, 2011 at 22:08, Lennart Poettering <lennart at poettering.net> wrote:
>> On Mon, 09.05.11 22:02, Lennart Poettering (lennart at poettering.net) wrote:
>> 
>>>> It's still in the 10 second range on a 600MHz cortex-a8 machine
>>>> booting from an SD card. I need to dig out my 400MHz arm920t to see
>>>> how long it takes there. So having udev-less operation in systemd
>>>> would be nice, even if it's only used on 'embedded'
>>> 
>>> Have you checked what precisely takes so long? My guess is that some
>>> driver has a slow sysfs uevent trigger callback, and that might be
>>> fixable in the driver. You might want to use strace with timestamps to
>>> figure out why udev trigger might be so slow.
>> 
>> Also note that only very few devices are exposed and depended on by
>> systemd. In an embedded env you might be able to simple trigger those
>> explicitly first, and then trigger the rest afterwards. That way you
>> don't have to wait 10s, and the triggering will be dispatched in the bg,
>> but you still get the flexibility that udev can handle hotplugged
>> devices.
>> 
>> Kay, opinions?
> 
> Guess that should work fine. I guess we could short-cut some stuff too
> if it helps for custom setups, so systemd would look if the device is
> already there, instead of wait for the tag to show up. But we would
> need to find out if that really helps.

Here's a systemd-analyze plot with udev 168: http://dominion.thruhere.net/koen/angstrom/systemd/168.svg

That's run on a beagleboard C3 running at 500Mhz on a 2GB sandisk SD card (±10MB/s read/write)

> Real numbers of the most recent udev on such systems would help, so we
> get an idea what we are dealing with.
> 
> Things like:
>  time (udevadm trigger; udevadm settle)
> would be good to know too. If that looks like something to fix, the output of:
>  udevadm monitor
> during the trigger command above will be useful too.

I'll do that later today.

regards,

Koen