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Date: Sun, 12 Jan 2014 17:22:48 +0100
From: Daniel Borkmann <dborkman@...hat.com>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org
Subject: [PATCH net-next 3/3] packet: use percpu mmap tx frame pending refcount
In PF_PACKET's packet mmap(), we can avoid using one atomic_inc()
and one atomic_dec() call in skb destructor and use a percpu
reference count instead in order to determine if packets are
still pending to be sent out. Micro-benchmark with [1] that has
been slightly modified (that is, protcol = 0 in socket(2) and
bind(2)), example on an i7-3520M machine:
./packet_mm_tx -s7000 -m7200 -z700000 em1, avg over 2500 runs:
With patch: 4,022,015 cyc
Without patch: 4,812,994 cyc
time ./packet_mm_tx -s64 -c10000000 em1 > /dev/null, stable:
With patch:
real 1m32.241s
user 0m0.287s
sys 1m29.316s
Without patch:
real 1m38.386s
user 0m0.265s
sys 1m35.572s
In function tpacket_snd(), it is okay to use packet_read_pending()
since in fast-path we short-circuit the condition already with
ph != NULL, since we have next frames to process.
In case we have MSG_DONTWAIT, we also do not execute this path as
need_wait is false here anyway, and in case of _no_ MSG_DONTWAIT
flag, it is okay to call a packet_read_pending(), because when
we ever reach that path, we're done processing frames anyway and
only look if there are skbs still outstanding to be orphaned.
The BUG_ON() in tpacket_destruct_skb() we can remove as well. It
can _only_ be set from inside tpacket_snd() path and we made
sure to increase tx_ring.pending in any case before we called
po->xmit(skb). So testing for tx_ring.pending == 0 is not too
useful. Instead, it would rather have been useful to test if
lower layers didn't orphan the skb so that we're missing ring
slots being put back to TP_STATUS_AVAILABLE. But such a bug will
be caught in user space already as we end up realizing that we do
not have any TP_STATUS_AVAILABLE slots left anymore. Therefore,
we're all set.
Btw, in case of RX_RING path, we do not make use of the pending
member, therefore we also don't need to use up any percpu memory
here.
[1] http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap
Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
---
net/packet/af_packet.c | 65 +++++++++++++++++++++++++++++++++++++++++++++-----
net/packet/diag.c | 1 +
net/packet/internal.h | 2 +-
3 files changed, 61 insertions(+), 7 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d5495d8..6803be98 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -89,6 +89,7 @@
#include <linux/errqueue.h>
#include <linux/net_tstamp.h>
#include <linux/reciprocal_div.h>
+#include <linux/percpu.h>
#ifdef CONFIG_INET
#include <net/inet_common.h>
#endif
@@ -1168,6 +1169,46 @@ static void packet_increment_head(struct packet_ring_buffer *buff)
buff->head = buff->head != buff->frame_max ? buff->head+1 : 0;
}
+static void packet_inc_pending(struct packet_ring_buffer *rb)
+{
+ this_cpu_inc(*rb->pending_refcnt);
+}
+
+static void packet_dec_pending(struct packet_ring_buffer *rb)
+{
+ this_cpu_dec(*rb->pending_refcnt);
+}
+
+static int packet_read_pending(const struct packet_ring_buffer *rb)
+{
+ int i, refcnt = 0;
+
+ /* We don't use pending refcount in rx_ring. */
+ if (rb->pending_refcnt == NULL)
+ return 0;
+
+ for_each_possible_cpu(i)
+ refcnt += *per_cpu_ptr(rb->pending_refcnt, i);
+
+ return refcnt;
+}
+
+static int packet_alloc_pending(struct packet_sock *po)
+{
+ po->rx_ring.pending_refcnt = NULL;
+
+ po->tx_ring.pending_refcnt = alloc_percpu(int);
+ if (unlikely(po->tx_ring.pending_refcnt == NULL))
+ return -ENOBUFS;
+
+ return 0;
+}
+
+static void packet_free_pending(struct packet_sock *po)
+{
+ free_percpu(po->tx_ring.pending_refcnt);
+}
+
static bool packet_rcv_has_room(struct packet_sock *po, struct sk_buff *skb)
{
struct sock *sk = &po->sk;
@@ -2014,8 +2055,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
__u32 ts;
ph = skb_shinfo(skb)->destructor_arg;
- BUG_ON(atomic_read(&po->tx_ring.pending) == 0);
- atomic_dec(&po->tx_ring.pending);
+ packet_dec_pending(&po->tx_ring);
ts = __packet_set_timestamp(po, ph, skb);
__packet_set_status(po, ph, TP_STATUS_AVAILABLE | ts);
@@ -2236,7 +2276,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
skb_set_queue_mapping(skb, packet_pick_tx_queue(dev));
skb->destructor = tpacket_destruct_skb;
__packet_set_status(po, ph, TP_STATUS_SENDING);
- atomic_inc(&po->tx_ring.pending);
+ packet_inc_pending(&po->tx_ring);
status = TP_STATUS_SEND_REQUEST;
err = po->xmit(skb);
@@ -2256,8 +2296,14 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
}
packet_increment_head(&po->tx_ring);
len_sum += tp_len;
- } while (likely((ph != NULL) || (need_wait &&
- atomic_read(&po->tx_ring.pending))));
+ } while (likely((ph != NULL) ||
+ /* Note: packet_read_pending() might be slow if we have
+ * to call it as it's per_cpu variable, but in fast-path
+ * we already short-circuit the loop with the first
+ * condition, and luckily don't have to go that path
+ * anyway.
+ */
+ (need_wait && packet_read_pending(&po->tx_ring))));
err = len_sum;
goto out_put;
@@ -2556,6 +2602,7 @@ static int packet_release(struct socket *sock)
/* Purge queues */
skb_queue_purge(&sk->sk_receive_queue);
+ packet_free_pending(po);
sk_refcnt_debug_release(sk);
sock_put(sk);
@@ -2717,6 +2764,10 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
po->num = proto;
po->xmit = dev_queue_xmit;
+ err = packet_alloc_pending(po);
+ if (err)
+ goto out2;
+
packet_cached_dev_reset(po);
sk->sk_destruct = packet_sock_destruct;
@@ -2749,6 +2800,8 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
preempt_enable();
return 0;
+out2:
+ sk_free(sk);
out:
return err;
}
@@ -3676,7 +3729,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
if (!closing) {
if (atomic_read(&po->mapped))
goto out;
- if (atomic_read(&rb->pending))
+ if (packet_read_pending(rb))
goto out;
}
diff --git a/net/packet/diag.c b/net/packet/diag.c
index a9584a2..533ce4f 100644
--- a/net/packet/diag.c
+++ b/net/packet/diag.c
@@ -3,6 +3,7 @@
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/packet_diag.h>
+#include <linux/percpu.h>
#include <net/net_namespace.h>
#include <net/sock.h>
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 0a87d7b..a47d5b5 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -64,7 +64,7 @@ struct packet_ring_buffer {
unsigned int pg_vec_pages;
unsigned int pg_vec_len;
- atomic_t pending;
+ int __percpu *pending_refcnt;
struct tpacket_kbdq_core prb_bdqc;
};
--
1.7.11.7
--
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