net: drop_monitor: make last_rx timestamp private

It was recently pointed out to me that the last_rx field of the
net_device structure wasn't updated regularly.  In fact only the
bonding driver really uses it currently.  Since the drop_monitor code
relies on the last_rx field to detect drops on recevie in hardware, We
need to find a more reliable way to rate limit our drop checks (so
that we don't check for drops on every frame recevied, which would be
inefficient.  This patch makes a last_rx timestamp that is private to
the drop monitor code and is updated for every device that we track.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 3 deletions

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index d31120248c03..0a113f26bc9f 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -52,6 +52,7 @@ struct per_cpu_dm_data {
 
 struct dm_hw_stat_delta {
         struct net_device *dev;
+        unsigned long last_rx;
         struct list_head list;
         struct rcu_head rcu;
         unsigned long last_drop_val;
@@ -180,18 +181,25 @@ static void trace_napi_poll_hit(struct napi_struct *napi)
         struct dm_hw_stat_delta *new_stat;
 
         /*
-         * Ratelimit our check time to dm_hw_check_delta jiffies
+         * Don't check napi structures with no associated device
          */
-        if (!napi->dev ||
-            !time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta))
+        if (!napi->dev)
                 return;
 
         rcu_read_lock();
         list_for_each_entry_rcu(new_stat, &hw_stats_list, list) {
+                /*
+                 * only add a note to our monitor buffer if:
+                 * 1) this is the dev we received on
+                 * 2) its after the last_rx delta
+                 * 3) our rx_dropped count has gone up
+                 */
                 if ((new_stat->dev == napi->dev)  &&
+                    (time_after(jiffies, new_stat->last_rx + dm_hw_check_delta)) &&
                     (napi->dev->stats.rx_dropped != new_stat->last_drop_val)) {
                         trace_drop_common(NULL, NULL);
                         new_stat->last_drop_val = napi->dev->stats.rx_dropped;
+                        new_stat->last_rx = jiffies;
                         break;
                 }
         }
@@ -287,6 +295,7 @@ static int dropmon_net_event(struct notifier_block *ev_block,
                         goto out;
 
                 new_stat->dev = dev;
+                new_stat->last_rx = jiffies;
                 INIT_RCU_HEAD(&new_stat->rcu);
                 spin_lock(&trace_state_lock);
                 list_add_rcu(&new_stat->list, &hw_stats_list);