netdev - [PATCH] drop_monitor: allow more events per second

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Date:	Thu, 19 Apr 2012 19:16:21 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>,
	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [PATCH] drop_monitor: allow more events per second

From: Eric Dumazet <edumazet@...gle.com>

It seems there is a logic error in trace_drop_common(), since we store
only 64 drops, even if they are from same location.

This fix is a one liner, but we probably need more work to avoid useless
atomic dec/inc

Now I can watch 1 Mpps drops through dropwatch...

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Neil Horman <nhorman@...driver.com>
---
Neil, it seems this code is not SMP/preempt safe. Worker can free our
data under us, and genlmsg_new() can return NULL under stress.

 net/core/drop_monitor.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 7f36b38..5c3c81a 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -150,6 +150,7 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
 	for (i = 0; i < msg->entries; i++) {
 		if (!memcmp(&location, msg->points[i].pc, sizeof(void *))) {
 			msg->points[i].count++;
+			atomic_inc(&data->dm_hit_count);
 			goto out;
 		}
 	}


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