AcoSail/kernel_optimize_test
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udp: elide zerocopy operation in hot path

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With MSG_ZEROCOPY, each skb holds a reference to a struct ubuf_info.
Release of its last reference triggers a completion notification.

The TCP stack in tcp_sendmsg_locked holds an extra ref independent of
the skbs, because it can build, send and free skbs within its loop,
possibly reaching refcount zero and freeing the ubuf_info too soon.

The UDP stack currently also takes this extra ref, but does not need
it as all skbs are sent after return from __ip(6)_append_data.

Avoid the extra refcount_inc and refcount_dec_and_test, and generally
the sock_zerocopy_put in the common path, by passing the initial
reference to the first skb.

This approach is taken instead of initializing the refcount to 0, as
that would generate error "refcount_t: increment on 0" on the
next skb_zcopy_set.

Changes
  v3 -> v4
    - Move skb_zcopy_set below the only kfree_skb that might cause
      a premature uarg destroy before skb_zerocopy_put_abort
      - Move the entire skb_shinfo assignment block, to keep that
        cacheline access in one place

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn 2018-11-30 15:32:40 -05:00 committed by David S. Miller
parent b5947e5d1e
commit 52900d2228
5 changed files with 36 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/skbuff.h
View File

@ -481,7 +481,7 @@ static inline void sock_zerocopy_get(struct ubuf_info *uarg)
}
void sock_zerocopy_put(struct ubuf_info *uarg);
void sock_zerocopy_put_abort(struct ubuf_info *uarg);
void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
void sock_zerocopy_callback(struct ubuf_info *uarg, bool success);
@ -1326,9 +1326,13 @@ static inline struct ubuf_info *skb_zcopy(struct sk_buff *skb)
return is_zcopy ? skb_uarg(skb) : NULL;
}
static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg)
static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg,
bool *have_ref)
{
if (skb && uarg && !skb_zcopy(skb)) {
if (unlikely(have_ref && *have_ref))
*have_ref = false;
else
sock_zerocopy_get(uarg);
skb_shinfo(skb)->destructor_arg = uarg;
skb_shinfo(skb)->tx_flags |= SKBTX_ZEROCOPY_FRAG;
@ -1374,7 +1378,7 @@ static inline void skb_zcopy_abort(struct sk_buff *skb)
struct ubuf_info *uarg = skb_zcopy(skb);
if (uarg) {
sock_zerocopy_put_abort(uarg);
sock_zerocopy_put_abort(uarg, false);
skb_shinfo(skb)->tx_flags &= ~SKBTX_ZEROCOPY_FRAG;
}
}

7
net/core/skbuff.c
View File

@ -1089,7 +1089,7 @@ void sock_zerocopy_put(struct ubuf_info *uarg)
}
EXPORT_SYMBOL_GPL(sock_zerocopy_put);
void sock_zerocopy_put_abort(struct ubuf_info *uarg)
void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
{
if (uarg) {
struct sock *sk = skb_from_uarg(uarg)->sk;
@ -1097,6 +1097,7 @@ void sock_zerocopy_put_abort(struct ubuf_info *uarg)
atomic_dec(&sk->sk_zckey);
uarg->len--;
if (have_uref)
sock_zerocopy_put(uarg);
}
}
@ -1137,7 +1138,7 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
return err;
}
skb_zcopy_set(skb, uarg);
skb_zcopy_set(skb, uarg, NULL);
return skb->len - orig_len;
}
EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);
@ -1157,7 +1158,7 @@ static int skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig,
if (skb_copy_ubufs(nskb, GFP_ATOMIC))
return -EIO;
}
skb_zcopy_set(nskb, skb_uarg(orig));
skb_zcopy_set(nskb, skb_uarg(orig), NULL);
}
return 0;
}

22
net/ipv4/ip_output.c
View File

@ -881,8 +881,8 @@ static int __ip_append_data(struct sock *sk,
int csummode = CHECKSUM_NONE;
struct rtable *rt = (struct rtable *)cork->dst;
unsigned int wmem_alloc_delta = 0;
bool paged, extra_uref;
u32 tskey = 0;
bool paged;
skb = skb_peek_tail(queue);
@ -921,12 +921,13 @@ static int __ip_append_data(struct sock *sk,
uarg = sock_zerocopy_realloc(sk, length, skb_zcopy(skb));
if (!uarg)
return -ENOBUFS;
extra_uref = true;
if (rt->dst.dev->features & NETIF_F_SG &&
csummode == CHECKSUM_PARTIAL) {
paged = true;
} else {
uarg->zerocopy = 0;
skb_zcopy_set(skb, uarg);
skb_zcopy_set(skb, uarg, &extra_uref);
}
}
@ -1015,13 +1016,6 @@ static int __ip_append_data(struct sock *sk,
skb->csum = 0;
skb_reserve(skb, hh_len);
/* only the initial fragment is time stamped */
skb_shinfo(skb)->tx_flags = cork->tx_flags;
cork->tx_flags = 0;
skb_shinfo(skb)->tskey = tskey;
tskey = 0;
skb_zcopy_set(skb, uarg);
/*
* Find where to start putting bytes.
*/
@ -1054,6 +1048,13 @@ static int __ip_append_data(struct sock *sk,
exthdrlen = 0;
csummode = CHECKSUM_NONE;
/* only the initial fragment is time stamped */
skb_shinfo(skb)->tx_flags = cork->tx_flags;
cork->tx_flags = 0;
skb_shinfo(skb)->tskey = tskey;
tskey = 0;
skb_zcopy_set(skb, uarg, &extra_uref);
if ((flags & MSG_CONFIRM) && !skb_prev)
skb_set_dst_pending_confirm(skb, 1);
@ -1124,13 +1125,12 @@ static int __ip_append_data(struct sock *sk,
if (wmem_alloc_delta)
refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
sock_zerocopy_put(uarg);
return 0;
error_efault:
err = -EFAULT;
error:
sock_zerocopy_put_abort(uarg);
sock_zerocopy_put_abort(uarg, extra_uref);
cork->length -= length;
IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTDISCARDS);
refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);

2
net/ipv4/tcp.c
View File

@ -1423,7 +1423,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
if (copied + copied_syn)
goto out;
out_err:
sock_zerocopy_put_abort(uarg);
sock_zerocopy_put_abort(uarg, true);
err = sk_stream_error(sk, flags, err);
/* make sure we wake any epoll edge trigger waiter */
if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 &&

22
net/ipv6/ip6_output.c
View File

@ -1258,7 +1258,7 @@ static int __ip6_append_data(struct sock *sk,
int csummode = CHECKSUM_NONE;
unsigned int maxnonfragsize, headersize;
unsigned int wmem_alloc_delta = 0;
bool paged;
bool paged, extra_uref;
skb = skb_peek_tail(queue);
if (!skb) {
@ -1327,12 +1327,13 @@ static int __ip6_append_data(struct sock *sk,
uarg = sock_zerocopy_realloc(sk, length, skb_zcopy(skb));
if (!uarg)
return -ENOBUFS;
extra_uref = true;
if (rt->dst.dev->features & NETIF_F_SG &&
csummode == CHECKSUM_PARTIAL) {
paged = true;
} else {
uarg->zerocopy = 0;
skb_zcopy_set(skb, uarg);
skb_zcopy_set(skb, uarg, &extra_uref);
}
}
@ -1454,13 +1455,6 @@ static int __ip6_append_data(struct sock *sk,
skb_reserve(skb, hh_len + sizeof(struct frag_hdr) +
dst_exthdrlen);
/* Only the initial fragment is time stamped */
skb_shinfo(skb)->tx_flags = cork->tx_flags;
cork->tx_flags = 0;
skb_shinfo(skb)->tskey = tskey;
tskey = 0;
skb_zcopy_set(skb, uarg);
/*
* Find where to start putting bytes
*/
@ -1492,6 +1486,13 @@ static int __ip6_append_data(struct sock *sk,
exthdrlen = 0;
dst_exthdrlen = 0;
/* Only the initial fragment is time stamped */
skb_shinfo(skb)->tx_flags = cork->tx_flags;
cork->tx_flags = 0;
skb_shinfo(skb)->tskey = tskey;
tskey = 0;
skb_zcopy_set(skb, uarg, &extra_uref);
if ((flags & MSG_CONFIRM) && !skb_prev)
skb_set_dst_pending_confirm(skb, 1);
@ -1562,13 +1563,12 @@ static int __ip6_append_data(struct sock *sk,
if (wmem_alloc_delta)
refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);
sock_zerocopy_put(uarg);
return 0;
error_efault:
err = -EFAULT;
error:
sock_zerocopy_put_abort(uarg);
sock_zerocopy_put_abort(uarg, extra_uref);
cork->length -= length;
IP6_INC_STATS(sock_net(sk), rt->rt6i_idev, IPSTATS_MIB_OUTDISCARDS);
refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc);