[PATCH net-next-2.6] loopback: Implement 64bit stats on 32bit arches

Eric Dumazet
2010-06-14T15:59:27Z

Uses a seqcount_t to synchronize stat producer and consumer, for packets
and bytes counter, now u64 types.

(dropped counter being rarely used, stay a native "unsigned long" type)

No noticeable performance impact on x86, as it only adds two increments
per frame. It might be more expensive on arches where smp_wmb() is not
free.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
drivers/net/loopback.c | 61 ++++++++++++++++++++++++++++++++-------
1 file changed, 51 insertions(+), 10 deletions(-)
diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 72b7949..09334f8 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -60,11 +60,51 @@
#include <net/net_namespace.h>

struct pcpu_lstats {
- unsigned long packets;
- unsigned long bytes;
+ u64 packets;
+ u64 bytes;
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+ seqcount_t seq;
+#endif
unsigned long drops;
};

+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+static void inline lstats_update_begin(struct pcpu_lstats *lstats)
+{
+ write_seqcount_begin(&lstats->seq);
+}
+static void inline lstats_update_end(struct pcpu_lstats *lstats)
+{
+ write_seqcount_end(&lstats->seq);
+}
+static void inline lstats_fetch_and_add(u64 *packets, u64 *bytes, const struct pcpu_lstats *lstats)
+{
+ u64 tpackets, tbytes;
+ unsigned int seq;
+
+ do {
+ seq = read_seqcount_begin(&lstats->seq);
+ tpackets = lstats->packets;
+ tbytes = lstats->bytes;
+ } while (read_seqcount_retry(&lstats->seq, seq));
+
+ *packets += tpackets;
+ *bytes += tbytes;
+}
+#else
+static void inline lstats_update_begin(struct pcpu_lstats *lstats)
+{
+}
+static void inline lstats_update_end(struct pcpu_lstats *lstats)
+{
+}
+static void inline lstats_fetch_and_add(u64 *packets, u64 *bytes, const struct pcpu_lstats *lstats)
+{
+ *packets += lstats->packets;
+ *bytes += lstats->bytes;
+}
+#endif
+
/*
* The higher levels take care of making this non-reentrant (it's
* called with bh's disabled).
@@ -86,21 +126,23 @@ static netdev_tx_t loopback_xmit(struct sk_buff *skb,

len = skb->len;
if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
+ lstats_update_begin(lb_stats);
lb_stats->bytes += len;
lb_stats->packets++;
+ lstats_update_end(lb_stats);
} else
lb_stats->drops++;

return NETDEV_TX_OK;
}

-static struct net_device_stats *loopback_get_stats(struct net_device *dev)
+static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev)
{
const struct pcpu_lstats __percpu *pcpu_lstats;
- struct net_device_stats *stats = &dev->stats;
- unsigned long bytes = 0;
- unsigned long packets = 0;
- unsigned long drops = 0;
+ struct rtnl_link_stats64 *stats = &dev->stats64;
+ u64 bytes = 0;
+ u64 packets = 0;
+ u64 drops = 0;
int i;

pcpu_lstats = (void __percpu __force *)dev->ml_priv;
@@ -108,8 +150,7 @@ static struct net_device_stats *loopback_get_stats(struct net_device *dev)
const struct pcpu_lstats *lb_stats;

lb_stats = per_cpu_ptr(pcpu_lstats, i);
- bytes += lb_stats->bytes;
- packets += lb_stats->packets;
+ lstats_fetch_and_add(&packets, &bytes, lb_stats);
drops += lb_stats->drops;
}
stats->rx_packets = packets;
@@ -158,7 +199,7 @@ static void loopback_dev_free(struct net_device *dev)
static const struct net_device_ops loopback_ops = {
.ndo_init = loopback_dev_init,
.ndo_start_xmit= loopback_xmit,
- .ndo_get_stats = loopback_get_stats,
+ .ndo_get_stats64 = loopback_get_stats64,
};

/*