Re: [PATCH] dev: use ifindex hash for dev_seq_ops

Instead of using the dev->next chain and trying to resync at each call to
dev_seq_start, use the ifindex, keeping the last index in seq->private field.

Tests revealed the following results for ifconfig > /dev/null
	* 1000 interfaces:
		* 0.114s without patch
		* 0.089s with patch
	* 3000 interfaces:
		* 0.489s without patch
		* 0.110s with patch
	* 5000 interfaces:
		* 1.363s without patch
		* 0.250s with patch
	* 128000 interfaces (other setup):
		* ~100s without patch
		* ~30s with patch

Signed-off-by: Mihai Maruseac <redacted>
---
 net/core/dev.c |   55 ++++++++++++++++++++++++++++++++++---------------------
 1 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 70ecb86..ea24445 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -4041,6 +4041,37 @@ static int dev_ifconf(struct net *net, char __user *arg)
 }
 
 #ifdef CONFIG_PROC_FS
+
+struct dev_iter_state {
+	struct seq_net_private p;
+	int ifindex;
+};
+
+static struct net_device *__dev_seq_next(struct seq_file *seq, loff_t *pos)
+{
+	struct dev_iter_state *state = seq->private;
+	struct net *net = seq_file_net(seq);
+	struct net_device *dev;
+	loff_t off;
+
+	dev = dev_get_by_index_rcu(net, state->ifindex);
+	if (likely(dev))
+		goto found;
+
+	off = 0;
+	for_each_netdev_rcu(net, dev)
+		if (off++ == *pos) {
+			state->ifindex = dev->ifindex;
+			goto found;
+		}
+
+	return NULL;
+found:
+	state->ifindex++;