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LPC: Booting Linux in five seconds
Posted Sep 25, 2008 7:55 UTC (Thu) by dlang (✭ supporter ✭, #313)
and most of the time it's not.
you have serialization on a lot of things
disk I/O (reading files, searching for the 50 places a config file could be before you find the one where it is, etc)
bus access (you can't query a PCI bus for multiple things at the same time)
timeouts (waiting after sending a command to see if something responds).
timeouts frequently combine with bus access as it may not be safe to do something else until you get a response from the device you just probed for (or decide that it's not really there)
and sometimes you do really have number crunching CPU tasks to do.
multi-core systems make a big difference if you really do have CPU as the limiting factor, but that's usually not the case (and IMHO software that has to do a lot of cpu work to just start up is probably in need of being fixed)
yes, when you get down into the low single-digit bootup range on a relativly slow COU (like the eepc from the talk), you do have to pay attention to the CPU load, but if you have similar systems otherwise, a fast cpu doesn't make that big a difference on a normal distro bootup
Posted Sep 25, 2008 14:39 UTC (Thu) by arjan (subscriber, #36785)
The key thing is to do the "critical path" of the boot sequential and as tightly packed as possible, while doing non-critical (to the boot) things asynchronous.
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