kernel: enhance realtime-ness when handling timeouts
The numbers of timeouts that expire on a given tick is arbitrary. When
handling them, interrupts were locked, which prevented higher-priority
interrupts from preempting the system clock timer handler.
Instead of looping on the list of timeouts, which needs interrupts being
locked since it can be manipulated at interrupt level, timeouts are
dequeued one by one, unlocking interrupts between each, and put on a
local 'expired' queue that is drained subsequently, with interrupts
unlocked. This scheme uses the fact that no timeout can be prepended
onto the timeout queue while expired timeouts are getting removed from
it, since adding a timeout of 0 is prohibited.
Timer handlers now run with interrupts unlocked: the previous behaviour
added potentially horrible non-determinism to the handling of timeouts.
Change-Id: I709085134029ea2ad73e167dc915b956114e14c2
Signed-off-by: Benjamin Walsh <walsh.benj@gmail.com>
5 files changed
