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SubjectRe: [PATCH 2/4] macvlan: cleanup rx statistics
Date
On Tuesday 24 November 2009 08:45:14 Arnd Bergmann wrote:
> On Tuesday 24 November 2009 08:15:53 Eric Dumazet wrote:
> > Arnd Bergmann a écrit :
> > I find following more readable, it probably generates more branches,
> > but avoid dirtying rx_errors if it is in another cache line.
> >
> > if (likely(success)) {
> > rx_stats->rx_packets++;
> > rx_stats->rx_bytes += length;
> > if (multicast)
> > rx_stats->multicast++;
> > } else {
> > rx_stats->rx_errors++;
> > }
>
> Given that the structure only has four members and alloc_percpu requests
> cache aligned data, it is rather likely to be in the same cache line.
>
> I'll have a look at what gcc generates on x86-64 for both versions
> and use the version you suggested unless it looks significantly more
> expensive.

Ok, that's what I got for trying to be clever. My version did not avoid
any branches, just created more code. I'll fold this update into my
patches then:
---
macvlan: cleanups

Use bool instead of int for flags, don't misoptimize rx counters,
avoid accessing a NULL skb.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 3db96b9..ff5f0b0 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -119,19 +119,23 @@ static int macvlan_addr_busy(const struct macvlan_port *port,
}

static inline void macvlan_count_rx(const struct macvlan_dev *vlan, int length,
- int success, int multicast)
+ bool success, bool multicast)
{
struct macvlan_rx_stats *rx_stats;

rx_stats = per_cpu_ptr(vlan->rx_stats, smp_processor_id());
- rx_stats->rx_packets += success != 0;
- rx_stats->rx_bytes += success ? length : 0;
- rx_stats->multicast += success && multicast;
- rx_stats->rx_errors += !success;
+ if (likely(success)) {
+ rx_stats->rx_packets++;;
+ rx_stats->rx_bytes += length;
+ if (multicast)
+ rx_stats->multicast++;
+ } else {
+ rx_stats->rx_errors++;
+ }
}

static int macvlan_broadcast_one(struct sk_buff *skb, struct net_device *dev,
- const struct ethhdr *eth, int local)
+ const struct ethhdr *eth, bool local)
{
if (!skb)
return NET_RX_DROP;
@@ -173,7 +177,7 @@ static void macvlan_broadcast(struct sk_buff *skb,
err = macvlan_broadcast_one(nskb, vlan->dev, eth,
mode == MACVLAN_MODE_BRIDGE);
macvlan_count_rx(vlan, skb->len + ETH_HLEN,
- likely(err == NET_RX_SUCCESS), 1);
+ err == NET_RX_SUCCESS, 1);
}
}
}
@@ -186,6 +190,7 @@ static struct sk_buff *macvlan_handle_frame(struct sk_buff *skb)
const struct macvlan_dev *vlan;
const struct macvlan_dev *src;
struct net_device *dev;
+ int len;

port = rcu_dereference(skb->dev->macvlan_port);
if (port == NULL)
@@ -218,8 +223,11 @@ static struct sk_buff *macvlan_handle_frame(struct sk_buff *skb)
kfree_skb(skb);
return NULL;
}
+ len = skb->len + ETH_HLEN;
skb = skb_share_check(skb, GFP_ATOMIC);
- macvlan_count_rx(vlan, skb->len + ETH_HLEN, likely(skb != NULL), 0);
+ macvlan_count_rx(vlan, len, skb != NULL, 0);
+ if (!skb)
+ return NULL;

skb->dev = dev;
skb->pkt_type = PACKET_HOST;
@@ -248,7 +256,7 @@ static int macvlan_queue_xmit(struct sk_buff *skb, struct net_device *dev)
int length = skb->len + ETH_HLEN;
int ret = dev_forward_skb(dest->dev, skb);
macvlan_count_rx(dest, length,
- likely(ret == NET_RX_SUCCESS), 0);
+ ret == NET_RX_SUCCESS, 0);

return NET_XMIT_SUCCESS;
}
--
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