Messages in this thread | | | Date | Wed, 13 May 2020 11:20:29 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 04/10] rcu: Implement rcu_segcblist_is_offloaded() config dependent |
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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?
> }; > > #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.
> /* > * 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;
> /* > @@ -78,7 +82,9 @@ static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg) > void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp); > void rcu_segcblist_init(struct rcu_segcblist *rsclp); > void rcu_segcblist_disable(struct rcu_segcblist *rsclp); > +#ifdef CONFIG_RCU_NOCB_CPU > void rcu_segcblist_offload(struct rcu_segcblist *rsclp); > +#endif
This can then remain unconditional.
> bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp); > bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp); > struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp); > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index d9a49cd6065a..804cf7dfff03 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -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.
> raw_lockdep_assert_held_rcu_node(rnp); > > @@ -1790,8 +1789,7 @@ static void rcu_gp_cleanup(void) > needgp = true; > } > /* Advance CBs to reduce false positives below. */ > - offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > - rcu_segcblist_is_offloaded(&rdp->cblist); > + offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
And here as well.
> if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) { > WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); > WRITE_ONCE(rcu_state.gp_req_activity, jiffies); > @@ -1985,8 +1983,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_data *rdp) > unsigned long flags; > unsigned long mask; > bool needwake = false; > - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > - rcu_segcblist_is_offloaded(&rdp->cblist); > + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
Ditto.
> struct rcu_node *rnp; > > rnp = rdp->mynode; > @@ -2153,8 +2150,7 @@ int rcutree_dead_cpu(unsigned int cpu) > static void rcu_do_batch(struct rcu_data *rdp) > { > unsigned long flags; > - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > - rcu_segcblist_is_offloaded(&rdp->cblist); > + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
Ditto.
> struct rcu_head *rhp; > struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); > long bl, count; > @@ -2397,8 +2393,7 @@ static __latent_entropy void rcu_core(void) > unsigned long flags; > struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); > struct rcu_node *rnp = rdp->mynode; > - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > - rcu_segcblist_is_offloaded(&rdp->cblist); > + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
Ditto.
> > if (cpu_is_offline(smp_processor_id())) > return; > @@ -2695,8 +2690,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) > rcu_segcblist_n_cbs(&rdp->cblist)); > > /* Go handle any RCU core processing required. */ > - if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > - unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { > + if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
Ditto.
> __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */ > } else { > __call_rcu_core(rdp, head, flags); > @@ -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???" ;-)
Thanx, Paul
> !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) > return 1; > > -- > 2.25.0 >
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