Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread wakeups

Paul E. McKenney
2014-07-02T17:57:30Z

On Wed, Jul 02, 2014 at 01:29:38PM -0400, Rik van Riel wrote:
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> On 07/02/2014 01:26 PM, Peter Zijlstra wrote:
> > On Wed, Jul 02, 2014 at 10:08:38AM -0700, Paul E. McKenney wrote:
> >> As were others, not that long ago. Today is the first hint that
> >> I got that you feel otherwise. But it does look like the softirq
> >> approach to callback processing needs to stick around for awhile
> >> longer. Nice to hear that softirq is now "sane and normal"
> >> again, I guess. ;-)
> >
> > Nah, softirqs are still totally annoying :-)
> >
> > So I've lost detail again, but it seems to me that on all CPUs that
> > are actually getting ticks, waking tasks to process the RCU state
> > is entirely over doing it. Might as well keep processing their RCU
> > state from the tick as was previously done.
>
> For CPUs that are not getting ticks (eg. because they are idle),
> is it worth waking up anything on that CPU, or would it make more
> sense to simply process their RCU callbacks on a different CPU,
> if there aren't too many pending?

Give or take the number of wakeups generated... ;-)

Thanx, Paul