Re: Use case for TASKS_RCU

[Steven Rostedt]

On Mon, 22 May 2017 17:00:36 -0700
"Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> > 
> > 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.  
> 
> And please see below for such a patch, which does add (just barely)
> fewer than 100 lines net.
> 
> Unfortunately, it does not work, as I should have known ahead of time
> from the dyntick-idle experience.  Not all context switches go through
> context_switch().  :-/

Wait. What context switch doesn't go through a context switch? Or do
you mean a user/kernel context switch?

-- Steve

> 
> I believe this is fixable, more or less like dyntick-idle's
> half-interrupts were fixable, but it will likely be a few days.  Not
> clear whether the result will be simpler than current TASKS_RCU, but
> there is only one way to find out.  ;-)
>