On Tue, Nov 13, 2012 at 12:56:54PM -0500, Nick Bowler wrote:

On 2012-11-13 09:08 -0800, Paul E. McKenney wrote:

quoted

On Tue, Nov 13, 2012 at 09:46:20AM -0500, Nick Bowler wrote:

quoted

On 2012-11-12 16:49 -0800, Paul E. McKenney wrote:

quoted

Hello!

I know of people using TINY_RCU, TREE_RCU, and TREE_PREEMPT_RCU, but I
have not heard of anyone using TINY_PREEMPT_RCU for whom TREE_PREEMPT_RCU
was not a viable option (in contrast, the people running Linux on
tiny-memmory systems typically use TINY_RCU).  Of course, if no one
really needs it, the proper thing to do is to remove it.

So, if you need TINY_PREEMPT_RCU, please let me know.  Otherwise, I will
remove it, probably in the 3.9 timeframe.

Yes, I use TINY_PREEMPT_RCU on my UP machines.  It is, in fact, the only
option.

Suppose that TREE_PREEMPT_RCU was available for !SMP && PREEMPT builds.
Would that work for you?

To be honest I don't really know what the difference is, other than what
the help text says, which is:

  [TINY_PREEMPT_RCU] greatly reduces the memory footprint of RCU.
  
"Greatly reduced memory footprint" sounds pretty useful...

OK, so from your viewpoint, the only possible benefit is smaller
memory?  How much memory does your device have, if I may ask?

As a side note, I wonder why any of these RCU implementations are
user-seclectable options in the first place?  It looks like you will
only ever have one choice, since the dependencies all seem mutually
exclusive:

  TREE_RCU         depends on !PREEMPT &&  SMP
  TREE_PREEMPT_RCU depends on  PREEMPT &&  SMP
  TINY_RCU         depends on !PREEMPT && !SMP
  TINY_PREEMPT_RCU depends on  PREEMPT && !SMP

Inertia on my part.  ;-)

							Thanx, Paul