net: gro: selective flush of packets
Current GRO can hold packets in gro_list for almost unlimited
time, in case napi->poll() handler consumes its budget over and over.
In this case, napi_complete()/napi_gro_flush() are not called.
Another problem is that gro_list is flushed in non friendly way :
We scan the list and complete packets in the reverse order.
(youngest packets first, oldest packets last)
This defeats priorities that sender could have cooked.
Since GRO currently only store TCP packets, we dont really notice the
bug because of retransmits, but this behavior can add unexpected
latencies, particularly on mice flows clamped by elephant flows.
This patch makes sure no packet can stay more than 1 ms in queue, and
only in stress situations.
It also complete packets in the right order to minimize latencies.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jesse Gross <jesse@nicira.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index de2bad7..d44668f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3471,17 +3471,31 @@
return netif_receive_skb(skb);
}
-inline void napi_gro_flush(struct napi_struct *napi)
+/* napi->gro_list contains packets ordered by age.
+ * youngest packets at the head of it.
+ * Complete skbs in reverse order to reduce latencies.
+ */
+void napi_gro_flush(struct napi_struct *napi, bool flush_old)
{
- struct sk_buff *skb, *next;
+ struct sk_buff *skb, *prev = NULL;
- for (skb = napi->gro_list; skb; skb = next) {
- next = skb->next;
- skb->next = NULL;
- napi_gro_complete(skb);
+ /* scan list and build reverse chain */
+ for (skb = napi->gro_list; skb != NULL; skb = skb->next) {
+ skb->prev = prev;
+ prev = skb;
}
- napi->gro_count = 0;
+ for (skb = prev; skb; skb = prev) {
+ skb->next = NULL;
+
+ if (flush_old && NAPI_GRO_CB(skb)->age == jiffies)
+ return;
+
+ prev = skb->prev;
+ napi_gro_complete(skb);
+ napi->gro_count--;
+ }
+
napi->gro_list = NULL;
}
EXPORT_SYMBOL(napi_gro_flush);
@@ -3542,6 +3556,7 @@
napi->gro_count++;
NAPI_GRO_CB(skb)->count = 1;
+ NAPI_GRO_CB(skb)->age = jiffies;
skb_shinfo(skb)->gso_size = skb_gro_len(skb);
skb->next = napi->gro_list;
napi->gro_list = skb;
@@ -3878,7 +3893,7 @@
if (unlikely(test_bit(NAPI_STATE_NPSVC, &n->state)))
return;
- napi_gro_flush(n);
+ napi_gro_flush(n, false);
local_irq_save(flags);
__napi_complete(n);
local_irq_restore(flags);
@@ -3983,8 +3998,17 @@
local_irq_enable();
napi_complete(n);
local_irq_disable();
- } else
+ } else {
+ if (n->gro_list) {
+ /* flush too old packets
+ * If HZ < 1000, flush all packets.
+ */
+ local_irq_enable();
+ napi_gro_flush(n, HZ >= 1000);
+ local_irq_disable();
+ }
list_move_tail(&n->poll_list, &sd->poll_list);
+ }
}
netpoll_poll_unlock(have);