Can anyone point me at any measurements and/or analysis of the cost of
moving back and forth between user and kernel space - when doing an
ioctl call into a driver, for example. Interested in current OpenSolaris
on x86-64 in particular.
I'm looking at the additional costs of sharing work between modules in
user and kernel space, trying to get some quantitative feel for how much
it costs to hop back and forth. It's obvious we want to minimise the
number of transitions, but I'd like some understanding of the numbers to
see how much effort it's worth putting into minimising them.
I'm also interested in other context switch costs - thread sleep and
wakeup principally. A much more complex area to analyse, but any
pointers to useful write-ups or measurements would be welcome.
Many Thanks,
jjf
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