Am 13.06.2015 um 13:33 schrieb Laurent Bercot:
> 30 seconds is a lot. What if you could get your desktop ready in
> 5 seconds or less ?

This would mean less than what most people think. Because everything
longer than half a second is perceived as being forced to wait. As long
as an improvement stays above this threshold, it just replaces one
forced wait with another forced wait.

In contrast an iPad is immediately ready to get work done. No perceived
wait. This feels like a different world! Good luck getting a PC from
sleep to online in half a second. As long as it is slower, the precise
number of seconds does not matter much.

If you want to make Linux go from sleep to ready faster, there is an
easier way: eliminate the waits in dhclient. The IP stack in a firmware
which I wrote initializes itself in a few milliseconds. The replies from
DHCP servers are lightning fast. Getting confirmation for the last used
IP address does not take significantly longer than a ping time. The only
slow parts are the waits in the recommended checks whether another PC is
errorneously using the same IP address. This is a very rare case, and
these cases can usually be detected within 10 milliseconds, because the
offending machine must be very nearby. Do just this quick check, then
report ready, and then do a more thorough check afterwards, just to be
closer to be RFC-compliant. Please make this as systemd-incompatible as
possible ;-) And then compare the whole sleep to useable time, not just
the time to show the desktop.

Btw. boot times tend to get less relevant in the future, because user
devices just never go completely offline, and servers are mostly
clusters. The whole upgrade downtime for the largest of my servers is
over 5 minutes (but only once a month). How much effort would I spend to
reduce this by 30 seconds? None! If the users want to get rid of this
downtime, they must order a cluster. And then the downtime of the single
machines would be completely irrelevant. There is no good reason to
completely rewrite Linux just to save a few seconds boot time.