Messages in this thread | | | Date | Tue, 13 Sep 2011 09:49:33 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/4] nohz: Split extended quiescent state handling from nohz switch |
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On Tue, Sep 13, 2011 at 02:06:45AM +0200, Frederic Weisbecker wrote: > On Wed, Sep 07, 2011 at 07:22:33AM -0700, Paul E. McKenney wrote: > > On Sun, Sep 04, 2011 at 04:36:43PM -0700, Paul E. McKenney wrote: > > > On Sat, Aug 20, 2011 at 07:30:49PM +0200, Frederic Weisbecker wrote: > > > > 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, split the tickless mode switching and > > > > RCU extended quiescent state logics. > > > > Make tick_nohz_stop/restart_sched_tick() RCU agnostic but provide > > > > a new pair of APIs tick_nohz_enter/exit_idle() that keep the > > > > old behaviour by handling both the nohz mode and RCU extended > > > > quiescent states, then convert every archs to use these. > > > > > > > > Archs that want to switch to RCU extended QS to some custom points > > > > can do it later by changing the parameter in tick_nohz_enter,exit_idle() > > > > to false and call rcu_enter,exit() separately. > > > > > > This approach looks quite good to me! A few comments below. > > > > But I get RCU stall warnings when running it on powerpc on top of > > the patch set at: > > > > https://lkml.org/lkml/2011/9/7/64 > > > > At first glance, it appears that CPUs are entering dyntick-idle > > mode without RCU being informed. Any thoughts on diagnostics? > > > > Thanx, Paul > > I've just tested with your rcu/next branch from github and applied > my patches on top of it but did not experience a stall in x86.
Thank you for checking this!
> That may be related to powerpc more precisely, or may be any arch > but on some particular condition.
OK, I guess my next step is to put a WARN_ON_ONCE() in the idle loop to check to see if there might be some other idle loop buried in PowerPC somewhere...
Thanx, Paul
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