Messages in this thread | | | Date | Thu, 14 May 2020 01:08:28 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 07/10] rcu: Temporarily assume that nohz full CPUs might not be NOCB |
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On Wed, May 13, 2020 at 11:25:27AM -0700, Paul E. McKenney wrote: > On Wed, May 13, 2020 at 06:47:11PM +0200, Frederic Weisbecker wrote: > > So far nohz_full CPUs had to be nocb. This requirement may change > > temporarily as we are working on preparing RCU to be able to toggle the > > nocb state of a CPU. Once that is done and nohz_full can be toggled as > > well dynamically, we'll restore that initial requirement. > > Would it simplify anything to make the CPU exit nohz_full first and > then exit rcu_nocb and vice versa in the other direction? That way the > assumption about nohz_full CPUs always being rcu_nocb could remain while > still allowing runtime changes to both states.
That's the future plan but for now nohz_full can't even be exited yet. RCU is unlucky enough to be chosen as the starting point of this whole work :-)
> Of course, given that setup, it would not be possible to cause a CPU to > exit rcu_nocb state if it was still in nohz_full state.
Right.
> My fear is that allowing a CPU to be in nohz_full state without also > being in rcu_nocb state will cause needless confusion and bug reports.
Well, it should only be visible to those who work on it since there won't be a proper interface before we achieve the whole.
Thanks.
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