On Tue, Jun 25, 2013 at 11:49:47PM +0200, Thomas Gleixner wrote:
> 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 ....
Woo-hoo!!! I will yank the NMI support on the next version. Thank
you for the info!
Thanx, Paul
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