On Tue, Oct 24, 2017 at 12:59:03PM +0200, Michal Hocko wrote:
> On Tue 24-10-17 03:02:09, tip-bot for Paul E. McKenney wrote:
> > Commit-ID: f79c3ad6189624c3de0ad5521610c9e22a1c33cf
> > Gitweb: https://git.kernel.org/tip/f79c3ad6189624c3de0ad5521610c9e22a1c33cf
> > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > AuthorDate: Wed, 30 Nov 2016 06:24:30 -0800
> > Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > CommitDate: Mon, 9 Oct 2017 14:25:17 -0700
> >
> > sched,rcu: Make cond_resched() provide RCU quiescent state
> >
> > There is some confusion as to which of cond_resched() or
> > cond_resched_rcu_qs() should be added to long in-kernel loops.
> > This commit therefore eliminates the decision by adding RCU quiescent
> > states to cond_resched(). This commit also simplifies the code that
> > used to interact with cond_resched_rcu_qs(), and that now interacts with
> > cond_resched(), to reduce its overhead. This reduction is necessary to
> > allow the heavier-weight cond_resched_rcu_qs() mechanism to be invoked
> > everywhere that cond_resched() is invoked.
> >
> > Part of that reduction in overhead converts the jiffies_till_sched_qs
> > kernel parameter to read-only at runtime, thus eliminating the need for
> > bounds checking.
>
> Thanks a lot Paul! I have just one question. Does the above mean that we
> can drop cond_resched_rcu_qs? Or there are still some scenarios when
> this is a better option?
Good point, and no time like the present! Please see commits cc1c305fff49
("netfilter: Eliminate cond_resched_rcu_qs() in favor of cond_resched()")
through cca9c4def233 ("rcu: Eliminate the cond_resched_rcu_qs()
definition") in my -rcu tree:
git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
Thanx, Paul
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