Messages in this thread | | | Date | Thu, 3 Nov 2011 12:54:33 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH RFC tip/core/rcu 19/28] nohz: Allow rcu extended quiescent state handling seperately from tick stop |
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On Wed, Nov 02, 2011 at 09:00:03PM -0700, Josh Triplett wrote: > On Wed, Nov 02, 2011 at 01:30:40PM -0700, Paul E. McKenney wrote: > > From: Frederic Weisbecker <fweisbec@gmail.com> > > > > It is assumed that rcu won't be used once we switch to tickless > > mode and until we restart the tick. However this is not always > > true, as in x86-64 where we dereference the idle notifiers after > > the tick is stopped. > > > > To prepare for fixing this, add two new APIs: > > tick_nohz_idle_enter_norcu() and tick_nohz_idle_exit_norcu(). > > > > If no use of RCU is made in the idle loop between > > tick_nohz_enter_idle() and tick_nohz_exit_idle() calls, the arch > > must instead call the new *_norcu() version such that the arch doesn't > > need to call rcu_idle_enter() and rcu_idle_exit(). > > The _norcu names confused me a bit. At first, I thought they meant > "idle but not RCU idle, so you can use RCU", but from re-reading the > commit message, apparently they mean "idle and RCU idle, so don't use > RCU". What about something like _forbid_rcu instead? Or, > alternatively, why not just go ahead and separate the two types of idle > entirely rather than introducing the _norcu variants first?
Or tick_nohz_idle_enter_rcu_stop() and tick_nohz_idle_exit_rcu_restart()?
Sounds clear but too long. May be we can shorten the tick_nohz thing in the beginning.
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