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Subject[PATCH] dev: use name hash for dev_seq_ops
Date
Instead of using the dev->next chain and trying to resync at each call to
dev_seq_start, use the name hash, keeping the bucket and the offset in
seq->private field.

The bucket number and the offset in the bucket are kept in a single unsigned
int value: pos = bucket << (32 - NETDEV_HASHBITS) + offset. When we reach the
end of the hash, both the bucket and the offset reach 0, so we need to test for
this in dev_seq_start to prevent endless loops.

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 <mmaruseac@ixiacom.com>
---
net/core/dev.c | 83 +++++++++++++++++++++++++++++++++++++++++++++----------
1 files changed, 68 insertions(+), 15 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 70ecb86..103eb28 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4041,6 +4041,59 @@ static int dev_ifconf(struct net *net, char __user *arg)
}

#ifdef CONFIG_PROC_FS
+
+struct dev_iter_state {
+ struct seq_net_private p;
+ unsigned int pos; /* bucket << 24 + offset */
+};
+
+#define BUCKET_SPACE (32 - NETDEV_HASHBITS)
+#define get_bucket(x) ((x) >> BUCKET_SPACE)
+#define get_offset(x) ((x) & ((1 << BUCKET_SPACE) - 1))
+#define set_bucket_offset(b, o) ((b) << BUCKET_SPACE | (o))
+
+static inline struct net_device *dev_from_same_bucket(struct seq_file *seq)
+{
+ struct dev_iter_state *state = seq->private;
+ struct net *net = seq_file_net(seq);
+ struct net_device *dev;
+ struct hlist_node *p;
+ struct hlist_head *h;
+ unsigned int count, bucket, offset;
+
+ bucket = get_bucket(state->pos);
+ offset = get_offset(state->pos);
+ h = &net->dev_name_head[bucket];
+ count = 0;
+ hlist_for_each_entry_rcu(dev, p, h, name_hlist) {
+ if (count++ == offset) {
+ state->pos = set_bucket_offset(bucket, count);
+ return dev;
+ }
+ }
+
+ return NULL;
+}
+
+static inline struct net_device *dev_from_new_bucket(struct seq_file *seq)
+{
+ struct dev_iter_state *state = seq->private;
+ struct net_device *dev;
+ unsigned int bucket;
+
+ bucket = get_bucket(state->pos);
+ do {
+ dev = dev_from_same_bucket(seq);
+ if (dev)
+ return dev;
+
+ bucket++;
+ state->pos = set_bucket_offset(bucket, 0);
+ } while (bucket < NETDEV_HASHENTRIES);
+
+ return NULL;
+}
+
/*
* This is invoked by the /proc filesystem handler to display a device
* in detail.
@@ -4048,33 +4101,33 @@ static int dev_ifconf(struct net *net, char __user *arg)
void *dev_seq_start(struct seq_file *seq, loff_t *pos)
__acquires(RCU)
{
- struct net *net = seq_file_net(seq);
- loff_t off;
- struct net_device *dev;
+ struct dev_iter_state *state = seq->private;

rcu_read_lock();
if (!*pos)
return SEQ_START_TOKEN;

- off = 1;
- for_each_netdev_rcu(net, dev)
- if (off++ == *pos)
- return dev;
+ /* check for end of the hash */
+ if (state->pos == 0 && *pos > 1)
+ return NULL;

- return NULL;
+ return dev_from_new_bucket(seq);
}

void *dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
- struct net_device *dev = v;
+ struct net_device *dev;
+
+ ++*pos;

if (v == SEQ_START_TOKEN)
- dev = first_net_device_rcu(seq_file_net(seq));
- else
- dev = next_net_device_rcu(dev);
+ return dev_from_new_bucket(seq);

- ++*pos;
- return dev;
+ dev = dev_from_same_bucket(seq);
+ if (dev)
+ return dev;
+
+ return dev_from_new_bucket(seq);
}

void dev_seq_stop(struct seq_file *seq, void *v)
@@ -4173,7 +4226,7 @@ static const struct seq_operations dev_seq_ops = {
static int dev_seq_open(struct inode *inode, struct file *file)
{
return seq_open_net(inode, file, &dev_seq_ops,
- sizeof(struct seq_net_private));
+ sizeof(struct dev_iter_state));
}

static const struct file_operations dev_seq_fops = {
--
1.7.4.1


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