This patch illustrates that the cpu timer can be used as
system timer on a SMP system:
1) count/compare on CPU 0 registers are used to generate
2) at the end of processing jiffy interrupt, cpu 0 sends
a special inter-processor interrupt (IPI) to all other
cpus and make them do process accounting stuff
3) count registers on all CPU 0 are sync'ed up at the beginning.
As a result we will have a consistent time reading on
all CPUs (do_gettimeofday()).
This patch assumes that the count registers on different CPUs
don't drift from each other after they sync up. If they do drift,
we can change the code to allow periodic sync up. We can
probably even support different count frequencies.
This patch is actually tested to be working on sibyte boards.
As a by-product of the patch we also fix a "gettimeofday() going backward"
problem on those smp boards.
P.S., the patch really looks more complicated than it should be, because
I am leaving the old time code for the board there but "ifdef"ed out.
If we make a complete transition to cpu timer, all the ifdef's and
old time code for the board should go away.
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