Messages in this thread | | | Date | Wed, 27 Sep 2006 09:18:47 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1] |
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On Wed, Sep 27, 2006 at 04:06:59PM +0200, Ingo Molnar wrote: > > * Eric W. Biederman <ebiederm@xmission.com> wrote: > > > I'm still wondering if we can move put_task_struct a little lower in > > the logic in the places where it is called, so it isn't called under a > > lock, or with preemption disabled. The only downside I see is that it > > might convolute the logic into unreadability. > > well it's all a function of the task reaping logic: right now we in > essence complete the reaping from the scheduler, via prev_state == > TASK_DEAD. We cannot do it sooner because the task is still in use. I > had one other implementation upstream some time ago, which was a > single-slot cache for reaped tasks - but that uglified other codepaths > because _something_ has to notice that the task has been unscheduled.
I believe that we are way too far into the task-teardown process for something like synchronize_rcu() to be feasible (not enough of the task left to be able to sleep!), but thought I should bring up the possibility on the off-chance that it caused someone to come up with a better approach.
Another possible approach would be workqueues. The disadvantages here are (1) higher overhead (2) workqueues can be delayed for a -long- time in a realtime environment, which increases vulnerability to memory exhaustion.
Again, hoping this provokes some better ideas...
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