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SubjectRe: [RFC v2 4/5] rcu: Use for_each_leaf_node_cpu() in force_qs_rnp()
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.king@canonical.com> and CoverityScan in
> a previous version of this patch.]

Nit: This note can go now that we use leaf_node_cpu_bit(). ;)

Thanks,
Mark.

> Signed-off-by: Boqun Feng <boqun.feng@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 4e5b81c843de..1ef13e63bc95 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
>

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