Messages in this thread | | | Date | Wed, 27 Jan 2010 03:59:27 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu] accelerate grace period if last non-dynticked CPU |
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On Wed, Jan 27, 2010 at 10:39:22PM +1100, Nick Piggin wrote: > On Wed, Jan 27, 2010 at 02:04:34AM -0800, Paul E. McKenney wrote: > > I could indeed do that. However, there is nothing stopping the > > more-active CPU from going into dynticks-idle mode between the time > > that I decide to push the callback to it and the time I actually do > > the pushing. :-( > > > > I considered pushing the callbacks to the orphanage, but that is a > > global lock that I would rather not acquire on each dyntick-idle > > transition. > > Well we already have to do atomic operations on the nohz mask, so > maybe it would be acceptable to actually have a spinlock there to > serialise operations on the nohz mask and also allow some subsystem > specific things (synchronisation here should allow either one of > those above approaches). > > It's not going to be zero cost, but seeing as there is already the > contended cacheline there, it's not going to introduce a > fundamentally new bottleneck.
Good point, although a contended global lock is nastier than a contended cache line.
Thanx, Paul
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