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author | Eric Dumazet <eric.dumazet@gmail.com> | 2009-06-11 02:55:43 -0700 |
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committer | David S. Miller <davem@davemloft.net> | 2009-06-11 02:55:43 -0700 |
commit | 2b85a34e911bf483c27cfdd124aeb1605145dc80 (patch) | |
tree | 3cea3e8a27b62de2f92e759641c27200d8bde421 /include | |
parent | f2333a014c1e13ac8e1b73a6fd77731c524eff78 (diff) | |
download | linux-stable-2b85a34e911bf483c27cfdd124aeb1605145dc80.tar.gz linux-stable-2b85a34e911bf483c27cfdd124aeb1605145dc80.tar.bz2 linux-stable-2b85a34e911bf483c27cfdd124aeb1605145dc80.zip |
net: No more expensive sock_hold()/sock_put() on each tx
One of the problem with sock memory accounting is it uses
a pair of sock_hold()/sock_put() for each transmitted packet.
This slows down bidirectional flows because the receive path
also needs to take a refcount on socket and might use a different
cpu than transmit path or transmit completion path. So these
two atomic operations also trigger cache line bounces.
We can see this in tx or tx/rx workloads (media gateways for example),
where sock_wfree() can be in top five functions in profiles.
We use this sock_hold()/sock_put() so that sock freeing
is delayed until all tx packets are completed.
As we also update sk_wmem_alloc, we could offset sk_wmem_alloc
by one unit at init time, until sk_free() is called.
Once sk_free() is called, we atomic_dec_and_test(sk_wmem_alloc)
to decrement initial offset and atomicaly check if any packets
are in flight.
skb_set_owner_w() doesnt call sock_hold() anymore
sock_wfree() doesnt call sock_put() anymore, but check if sk_wmem_alloc
reached 0 to perform the final freeing.
Drawback is that a skb->truesize error could lead to unfreeable sockets, or
even worse, prematurely calling __sk_free() on a live socket.
Nice speedups on SMP. tbench for example, going from 2691 MB/s to 2711 MB/s
on my 8 cpu dev machine, even if tbench was not really hitting sk_refcnt
contention point. 5 % speedup on a UDP transmit workload (depends
on number of flows), lowering TX completion cpu usage.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r-- | include/net/sock.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/include/net/sock.h b/include/net/sock.h index 4bb1ff9fd15b..010e14a93c92 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1217,9 +1217,13 @@ static inline int skb_copy_to_page(struct sock *sk, char __user *from, static inline void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) { - sock_hold(sk); skb->sk = sk; skb->destructor = sock_wfree; + /* + * We used to take a refcount on sk, but following operation + * is enough to guarantee sk_free() wont free this sock until + * all in-flight packets are completed + */ atomic_add(skb->truesize, &sk->sk_wmem_alloc); } |