On Mon, Oct 17, 2005 at 08:42:05AM -0700, Linus Torvalds wrote:
>
> On Mon, 17 Oct 2005, Dipankar Sarma wrote:
>
> > This I am not sure, it is Linus' call. I am just trying to do the
> > right thing - fix the real problem.
>
> It sure looks like the batch limiter is the fundamental problem.
>
> Instead of limiting the batching, we should likely try to avoid the RCU
> lists getting huge in the first place - ie do the RCU callback processing
> more often if the list is getting longer.
>
> So I suspect that the _real_ fix is:
>
> - for 2.6.14: remove the batching limig (or just make it much higher for
> now)
You can remove the batching limit by making maxbatch = 0 by default.
Just a one line patch.
> - post-14: work on making sure rcu callbacks are done in a more timely
> manner when the rcu queue gets long. This would involve TIF_RCUPENDING
> and whatever else to make sure that we have timely quiescent periods,
> and we do the RCU callback tasklet more often if the queue is long.
Yes, I am already looking at this. There are a number approaches
to this include adaptive algorithm to cater to naughty corner
cases and/or adding different ways to handle RCU as in
tree. I hope to experiment with these incrementally after 2.6.14 over
a period of time and see what works best for most people.
Thanks
Dipankar
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