The following commit has been merged into the core/rcu branch of tip: Commit-ID: abfce0414814149f716e1d30da1fb3140d1b3473 Gitweb: https://git.kernel.org/tip/abfce0414814149f716e1d30da1fb3140d1b3473 Author: Wei Yang <richard.weiyang@xxxxxxxxx> AuthorDate: Sun, 19 Apr 2020 21:57:15 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Mon, 29 Jun 2020 11:58:49 -07:00 rcu: Simplify the calculation of rcu_state.ncpus There is only 1 bit set in mask, which means that the only difference between oldmask and the new one will be at the position where the bit is set in mask. This commit therefore updates rcu_state.ncpus by checking whether the bit in mask is already set in rnp->expmaskinitnext. Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/tree.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 6c6569e..bef1dc9 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3842,10 +3842,9 @@ void rcu_cpu_starting(unsigned int cpu) { unsigned long flags; unsigned long mask; - int nbits; - unsigned long oldmask; struct rcu_data *rdp; struct rcu_node *rnp; + bool newcpu; if (per_cpu(rcu_cpu_started, cpu)) return; @@ -3857,12 +3856,10 @@ void rcu_cpu_starting(unsigned int cpu) mask = rdp->grpmask; raw_spin_lock_irqsave_rcu_node(rnp, flags); WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); - oldmask = rnp->expmaskinitnext; + newcpu = !(rnp->expmaskinitnext & mask); rnp->expmaskinitnext |= mask; - oldmask ^= rnp->expmaskinitnext; - nbits = bitmap_weight(&oldmask, BITS_PER_LONG); /* Allow lockless access for expedited grace periods. */ - smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */ + smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */ ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus); rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
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