On Tue, 25 Jun 2013, Paul E. McKenney wrote:
> Note that this version pays attention to CPUs that have taken an NMI
> from idle. It is not clear to me that NMI handlers can safely access
> the time on a system that is long-term idle. Unless someone tells me
> that it is somehow safe to access time from an NMI from idle, I will
> remove NMI support in the next version.
NMI cannot access any time related functions independent of NOHZ, long
term idle or whatever you come up with:
write_seqcount_begin(&timekeeper_seq);
---> NMI
...
do {
seq = read_seqcount_begin(&timekeeper_seq);
} while (read_seqcount_retry(&timekeeper_seq, seq));
Guess how well that works ....
Thanks,
tglx
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