On Thu, Dec 15, 2016 at 02:51:36PM +0000, Colin Ian King wrote: > On 15/12/16 14:42, Boqun Feng wrote: > > On Thu, Dec 15, 2016 at 12:04:59PM +0000, Mark Rutland wrote: > >> On Thu, Dec 15, 2016 at 10:42:03AM +0800, Boqun Feng wrote: > >>> ->qsmask of an RCU leaf node is usually more sparse than the > >>> corresponding cpu_possible_mask. So replace the > >>> for_each_leaf_node_possible_cpu() in force_qs_rnp() with > >>> for_each_leaf_node_cpu() to save several checks. > >>> > >>> [Note we need to use "1UL << bit" instead of "1 << bit" to generate the > >>> corresponding mask for a bit because @mask is unsigned long, this was > >>> spotted by Colin Ian King <colin.k...@canonical.com> and CoverityScan in > >>> a previous version of this patch.] > >> > >> Nit: This note can go now that we use leaf_node_cpu_bit(). ;) > >> > > > > I kinda keep this here for honoring the effort of finding out this bug > > from Colin, but yes, it's no longer needed here for the current code. > > Yep, remove it. >
Paul, here is a modified version of this patch, what I only did is removing this note. Besides I rebased the whole series on the current rcu/dev branch of -rcu tree, on this very commit: 8e9b2521b18a ("doc: Quick-Quiz answers are now inline") And I put the latest version at git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git leaf-node If you thought it's better, I could send a v3 ;-) Regards, Boqun ------------------------>8 From: Boqun Feng <boqun.f...@gmail.com> Date: Thu, 8 Dec 2016 23:21:11 +0800 Subject: [PATCH v2.1 4/5] rcu: Use for_each_leaf_node_cpu() in force_qs_rnp() ->qsmask of an RCU leaf node is usually more sparse than the corresponding cpu_possible_mask. So replace the for_each_leaf_node_possible_cpu() in force_qs_rnp() with for_each_leaf_node_cpu() to save several checks. Signed-off-by: Boqun Feng <boqun.f...@gmail.com> --- kernel/rcu/tree.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 4ea4496f4ecc..c2b753fb7f09 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3046,13 +3046,11 @@ static void force_qs_rnp(struct rcu_state *rsp, continue; } } - for_each_leaf_node_possible_cpu(rnp, cpu) { - unsigned long bit = leaf_node_cpu_bit(rnp, cpu); - if ((rnp->qsmask & bit) != 0) { - if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj)) - mask |= bit; - } - } + + for_each_leaf_node_cpu(rnp, rnp->qsmask, cpu) + if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj)) + mask |= leaf_node_cpu_bit(rnp, cpu); + if (mask != 0) { /* Idle/offline CPUs, report (releases rnp->lock. */ rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); -- 2.10.2