Messages in this thread | | | Date | Fri, 19 May 2017 12:06:09 -0700 | From | "Paul E. McKenney" <> | Subject | Re: Use case for TASKS_RCU |
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On Fri, May 19, 2017 at 10:23:31AM -0400, Steven Rostedt wrote: > On Fri, 19 May 2017 10:04:21 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > On Fri, 19 May 2017 06:35:50 -0700 > > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > > > > > Simpler would be better! > > > > > > However, is it really guaranteed that one SCHED_IDLE thread cannot > > > preempt another? If not, then the trampoline-freeing SCHED_IDLE thread > > > might preempt some other SCHED_IDLE thread in the middle of a trampoline. > > > I am not seeing anything that prevents such preemption, but it is rather > > > early local time, so I could easily be missing something. > > > > > > However, if SCHED_IDLE threads cannot preempt other threads, even other > > > SCHED_IDLE threads, then your approach sounds quite promising to me. > > > > > > Steve, Peter, thoughts? > > > > SCHED_IDLE is the swapper task. There's one on each CPU, and they don't > > migrate. And they only get called when there's no other task running. > > Peter just "schooled" me on IRC. I stand corrected (and he may respond > to this email too). I guess any task can become SCHED_IDLE. > > But that just makes this an even less likely option for > synchronize_rcu_tasks().
Hmmm... The goal is to make sure that any task that was preempted or running at a given point in time passes through a voluntary context switch (or userspace execution, or, ...).
What is the simplest way to get this job done? To Ingo's point, I bet that there is a simpler way than the current TASKS_RCU implementation.
Ingo, if I make it fit into 100 lines of code, would you be OK with it? I probably need a one-line hook at task-creation time and another at task-exit time, if that makes a difference.
Thanx, Paul
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