Messages in this thread | | | Date | Thu, 14 May 2020 08:47:54 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 04/10] rcu: Implement rcu_segcblist_is_offloaded() config dependent |
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On Thu, May 14, 2020 at 01:03:31AM +0200, Frederic Weisbecker wrote: > On Wed, May 13, 2020 at 11:20:29AM -0700, Paul E. McKenney wrote: > > On Wed, May 13, 2020 at 06:47:08PM +0200, Frederic Weisbecker wrote: > > > This simplify the usage of this API and avoid checking the kernel > > > config from the callers. > > > > > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > > > Cc: Paul E. McKenney <paulmck@kernel.org> > > > Cc: Josh Triplett <josh@joshtriplett.org> > > > Cc: Steven Rostedt <rostedt@goodmis.org> > > > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > > Cc: Lai Jiangshan <jiangshanlai@gmail.com> > > > Cc: Joel Fernandes <joel@joelfernandes.org> > > > --- > > > include/linux/rcu_segcblist.h | 2 ++ > > > kernel/rcu/rcu_segcblist.c | 2 ++ > > > kernel/rcu/rcu_segcblist.h | 6 ++++++ > > > kernel/rcu/tree.c | 21 +++++++-------------- > > > 4 files changed, 17 insertions(+), 14 deletions(-) > > > > > > diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h > > > index b36afe7b22c9..0ced0a0ecbcf 100644 > > > --- a/include/linux/rcu_segcblist.h > > > +++ b/include/linux/rcu_segcblist.h > > > @@ -73,7 +73,9 @@ struct rcu_segcblist { > > > long len; > > > #endif > > > u8 enabled; > > > +#ifdef CONFIG_RCU_NOCB_CPU > > > u8 offloaded; > > > +#endif > > > > Given that this is only one byte and that removing it won't actually > > save any memory on most architectures, why not just leave it and > > adjust as shown below? > > Right, the point was to make it private to that config and trigger > a build error otherwise. But if we have an off case that's fine. > > > > > > }; > > > > > > #define RCU_SEGCBLIST_INITIALIZER(n) \ > > > diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c > > > index 9a0f66133b4b..d8ea2bef5574 100644 > > > --- a/kernel/rcu/rcu_segcblist.c > > > +++ b/kernel/rcu/rcu_segcblist.c > > > @@ -166,6 +166,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp) > > > rsclp->enabled = 0; > > > } > > > > > > +#ifdef CONFIG_RCU_NOCB_CPU > > > /* > > > * Mark the specified rcu_segcblist structure as offloaded. This > > > * structure must be empty. > > > @@ -174,6 +175,7 @@ void rcu_segcblist_offload(struct rcu_segcblist *rsclp) > > > { > > > rsclp->offloaded = 1; > > > } > > > +#endif > > > > Leave this unconditional, as it is nowhere near a fastpath. > > The point was to not raise false hopes to those who want to > offload when it's not supported. > > Let's perhaps have at least a WARN_ON_ONCE(1) if it is called > when !CONFIG_RCU_NOCB_CPU ?
Sounds like a good choice to me!
> > > /* > > > * Does the specified rcu_segcblist structure contain callbacks that > > > diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h > > > index 5c293afc07b8..4c1503a82492 100644 > > > --- a/kernel/rcu/rcu_segcblist.h > > > +++ b/kernel/rcu/rcu_segcblist.h > > > @@ -62,7 +62,11 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp) > > > /* Is the specified rcu_segcblist offloaded? */ > > > static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp) > > > { > > > +#ifdef CONFIG_RCU_NOCB_CPU > > > return rsclp->offloaded; > > > +#else > > > + return false; > > > +#endif > > > } > > > > Then this can just be: > > > > return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded; > > Ok. > > > > @@ -1401,8 +1401,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) > > > { > > > bool ret = false; > > > bool need_qs; > > > - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > > > - rcu_segcblist_is_offloaded(&rdp->cblist); > > > + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); > > > > The adjustment to rcu_segcblist_is_offloaded() allows this (welcome!) > > simplification to remain. > > Ok thanks! > > > > @@ -3243,8 +3237,7 @@ static int rcu_pending(int user) > > > > > > /* Has RCU gone idle with this CPU needing another grace period? */ > > > if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) && > > > - (!IS_ENABLED(CONFIG_RCU_NOCB_CPU) || > > > - !rcu_segcblist_is_offloaded(&rdp->cblist)) && > > > + !rcu_segcblist_is_offloaded(&rdp->cblist) && > > > > Ditto. > > > > As in "Why didn't I do it that way to start with???" ;-) > > You say that to someone who's too lazy to script short commands typed > 100 times a day ;-)
;-) ;-) ;-)
Thanx, Paul
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