Messages in this thread | | | Date | Fri, 7 Jul 2006 16:15:24 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH -rt] catch put_task_struct RCU handling up to mainline |
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On Fri, Jul 07, 2006 at 11:56:00PM +0100, Esben Nielsen wrote: > On Fri, 7 Jul 2006, Paul E. McKenney wrote: > > >Hello! > > > >Due to the separate -rt and mainline evolution of RCU signal handling, > >the -rt patchset now makes each task struct go through two RCU grace > >periods, with one call_rcu() in release_task() and with another > >in put_task_struct(). Only the call_rcu() in release_task() is > >required, since this is the one that is associated with tearing down > >the task structure. > > > >This patch removes the extra call_rcu() in put_task_struct(), synching > >this up with mainline. Tested lightly on i386. > > > > The extra call_rcu() has an advantage: > It defers work away from the task doing the last put_task_struct(). > It could be a priority 99 task with hard latency requirements doing > some PI boosting, forinstance. The extra call_rcu() defers non-RT work to > a low priority task. This is in generally a very good idea in a real-time > system. > So unless you can argue that the work defered is as small as the work of > doing a call_rcu() I would prefer the extra call_rcu().
I would instead argue that the only way that the last put_task_struct() is an unrelated high-priority task is if it manipulating an already-exited task. In particular, I believe that the sys_exit() path prohibits your example of priority-boosting an already-exited task by removing the exiting task from the various lists before doing the release_task() on itself.
Please let me know what I am missing here!
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