Re: [PATCH RFC nohz_full 0/8] Provide infrastructure for full-system idle

[Thomas Gleixner <tglx@linutronix.de>]

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