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Date: Thu, 27 Mar 2014 16:38:30 +0100
From: Daniel Borkmann <dborkman@...hat.com>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org, Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [PATCH net-next] packet: respect devices with LLTX flag in direct xmit
Quite often it can be useful to test with dummy or similar
devices as a blackhole sink for skbs. Such devices are only
equipped with a single txq, but marked as NETIF_F_LLTX as
they do not require locking their internal queues on xmit
(or implement locking themselves). Therefore, rather use
HARD_TX_{UN,}LOCK API, so that NETIF_F_LLTX will be respected.
trafgen mmap/TX_RING example against dummy device with config
foo: { fill(0xff, 64) } results in the following performance
improvements for such scenarios on an ordinary Core i7/2.80GHz:
Before:
Performance counter stats for 'trafgen -i foo -o du0 -n100000000' (10 runs):
160,975,944,159 instructions:k # 0.55 insns per cycle ( +- 0.09% )
293,319,390,278 cycles:k # 0.000 GHz ( +- 0.35% )
192,501,104 branch-misses:k ( +- 1.63% )
831 context-switches:k ( +- 9.18% )
7 cpu-migrations:k ( +- 7.40% )
69,382 cache-misses:k # 0.010 % of all cache refs ( +- 2.18% )
671,552,021 cache-references:k ( +- 1.29% )
22.856401569 seconds time elapsed ( +- 0.33% )
After:
Performance counter stats for 'trafgen -i foo -o du0 -n100000000' (10 runs):
133,788,739,692 instructions:k # 0.92 insns per cycle ( +- 0.06% )
145,853,213,256 cycles:k # 0.000 GHz ( +- 0.17% )
59,867,100 branch-misses:k ( +- 4.72% )
384 context-switches:k ( +- 3.76% )
6 cpu-migrations:k ( +- 6.28% )
70,304 cache-misses:k # 0.077 % of all cache refs ( +- 1.73% )
90,879,408 cache-references:k ( +- 1.35% )
11.719372413 seconds time elapsed ( +- 0.24% )
Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
Cc: Jesper Dangaard Brouer <brouer@...hat.com>
---
net/packet/af_packet.c | 40 ++++++++++++++++++++--------------------
1 file changed, 20 insertions(+), 20 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 097a354..01039d2 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -243,40 +243,40 @@ static int packet_direct_xmit(struct sk_buff *skb)
const struct net_device_ops *ops = dev->netdev_ops;
netdev_features_t features;
struct netdev_queue *txq;
+ int ret = NETDEV_TX_BUSY;
u16 queue_map;
- int ret;
if (unlikely(!netif_running(dev) ||
- !netif_carrier_ok(dev))) {
- kfree_skb(skb);
- return NET_XMIT_DROP;
- }
+ !netif_carrier_ok(dev)))
+ goto drop;
features = netif_skb_features(skb);
if (skb_needs_linearize(skb, features) &&
- __skb_linearize(skb)) {
- kfree_skb(skb);
- return NET_XMIT_DROP;
- }
+ __skb_linearize(skb))
+ goto drop;
queue_map = skb_get_queue_mapping(skb);
txq = netdev_get_tx_queue(dev, queue_map);
- __netif_tx_lock_bh(txq);
- if (unlikely(netif_xmit_frozen_or_stopped(txq))) {
- ret = NETDEV_TX_BUSY;
- kfree_skb(skb);
- goto out;
+ local_bh_disable();
+
+ HARD_TX_LOCK(dev, txq, smp_processor_id());
+ if (!netif_xmit_frozen_or_stopped(txq)) {
+ ret = ops->ndo_start_xmit(skb, dev);
+ if (ret == NETDEV_TX_OK)
+ txq_trans_update(txq);
}
+ HARD_TX_UNLOCK(dev, txq);
- ret = ops->ndo_start_xmit(skb, dev);
- if (likely(dev_xmit_complete(ret)))
- txq_trans_update(txq);
- else
+ local_bh_enable();
+
+ if (!dev_xmit_complete(ret))
kfree_skb(skb);
-out:
- __netif_tx_unlock_bh(txq);
+
return ret;
+drop:
+ kfree_skb(skb);
+ return NET_XMIT_DROP;
}
static struct net_device *packet_cached_dev_get(struct packet_sock *po)
--
1.7.11.7
--
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