From 27b75c95f10d249574d9c4cb9dab878107faede8 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 15 Oct 2010 05:44:11 +0000 Subject: net: avoid RCU for NOCACHE dst There is no point using RCU for dst we allocate for a very short time (used once). Change dst_release() to take DST_NOCACHE into account, but also change skb_dst_set_noref() to force a refcount increment for such dst. This is a _huge_ gain, because we dont waste memory to store xx thousand of dsts. Instead of queueing them to RCU, we can free them instantly. CPU caches can stay hot, re-using same memory blocks to hold temporary dsts. Note : remove unneeded smp_mb__before_atomic_dec(); in dst_release(), since atomic_dec_return() implies a full memory barrier. Stress test, 160.000.000 udp frames sent, IP route cache disabled (DDOS). Before: real 0m38.091s user 0m13.189s sys 7m53.018s After: real 0m29.946s user 0m12.157s sys 7m40.605s For reference, if IP route cache was enabled : real 0m32.030s user 0m10.521s sys 8m15.243s Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/route.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) (limited to 'net/ipv4/route.c') diff --git a/net/ipv4/route.c b/net/ipv4/route.c index ff98983d2a4..d6cb2bfcd8e 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1105,9 +1105,9 @@ restart: * Note that we do rt_free on this new route entry, so that * once its refcount hits zero, we are still able to reap it * (Thanks Alexey) - * Note also the rt_free uses call_rcu. We don't actually - * need rcu protection here, this is just our path to get - * on the route gc list. + * Note: To avoid expensive rcu stuff for this uncached dst, + * we set DST_NOCACHE so that dst_release() can free dst without + * waiting a grace period. */ rt->dst.flags |= DST_NOCACHE; @@ -1117,12 +1117,11 @@ restart: if (net_ratelimit()) printk(KERN_WARNING "Neighbour table failure & not caching routes.\n"); - rt_drop(rt); + ip_rt_put(rt); return err; } } - rt_free(rt); goto skip_hashing; } -- cgit v1.2.3-18-g5258