Messages in this thread | | | Date | Thu, 13 Apr 2017 12:42:28 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 04/13] rcu: Make RCU_FANOUT_LEAF help text more explicit about skew_tick |
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On Thu, Apr 13, 2017 at 08:29:39PM +0200, Peter Zijlstra wrote: > On Thu, Apr 13, 2017 at 10:31:00AM -0700, Paul E. McKenney wrote: > > On Thu, Apr 13, 2017 at 07:04:34PM +0200, Peter Zijlstra wrote: > > > > And I have vague memories of it actually causing lock contention, but > > > I've forgotten how that worked. > > > > That is a new one on me. I can easily see how not skewing ticks could > > cause serious lock contention, but am missing how skewed ticks would > > do so. > > It could've been something like cacheline bouncing. Where with a > synchronized tick, the (global) cacheline would get used by all CPUs on > a node before heading out to the next node etc.. Where with a skewed > tick, it would forever bounce around.
In other words, motivating the order of the skewed ticks to be guided by hardware locality?
Thanx, Paul
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