| Message ID | cfd580d15d1bbf7ba294f2f49266ae5ded02fec7.1705836321.git.pabeni@redhat.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Delegated to: | Mat Martineau |
| Headers | show |
| Series | mptcp: implement TCP_NOTSENT_LOWAT support | expand |
On Mon, 22 Jan 2024, Paolo Abeni wrote: > Add support for such socket option storing the user-space provided > value in a new msk field, and using such data to implement the > _mptcp_stream_memory_free() helper, similar to the TCP one. > > To avoid adding more indirect calls in the fast path, instead of > hooking the new helper via the sk_stream_memory_free sock cb, > add the directly calls where needed. > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/464 > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > --- > net/mptcp/protocol.c | 33 ++++++++++++++++++++++++++++----- > net/mptcp/protocol.h | 28 +++++++++++++++++++++++++++- > net/mptcp/sockopt.c | 12 ++++++++++++ > 3 files changed, 67 insertions(+), 6 deletions(-) > > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c > index 3599205fdceb..53d6c5544900 100644 > --- a/net/mptcp/protocol.c > +++ b/net/mptcp/protocol.c > @@ -1761,6 +1761,25 @@ static int do_copy_data_nocache(struct sock *sk, int copy, > return 0; > } > > +static u32 mptcp_send_limit(const struct sock *sk) > +{ > + const struct mptcp_sock *msk = mptcp_sk(sk); > + u32 limit, not_sent; > + > + if (!sk_stream_memory_free(sk)) > + return 0; > + > + limit = mptcp_notsent_lowat(sk); > + if (limit == UINT_MAX) > + return UINT_MAX; > + > + not_sent = msk->write_seq - msk->snd_nxt; > + if (not_sent >= limit) > + return 0; > + > + return limit - not_sent; > +} > + > static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > { > struct mptcp_sock *msk = mptcp_sk(sk); > @@ -1805,6 +1824,12 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > struct mptcp_data_frag *dfrag; > bool dfrag_collapsed; > size_t psize, offset; > + u32 copy_limit; > + > + /* ensure fitting the notsent_lowat() constraint */ > + copy_limit = mptcp_send_limit(sk); > + if (!copy_limit) > + goto wait_for_memory; > > /* reuse tail pfrag, if possible, or carve a new one from the > * page allocator > @@ -1812,9 +1837,6 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > dfrag = mptcp_pending_tail(sk); > dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag); > if (!dfrag_collapsed) { > - if (!sk_stream_memory_free(sk)) > - goto wait_for_memory; > - > if (!mptcp_page_frag_refill(sk, pfrag)) > goto wait_for_memory; > > @@ -1829,6 +1851,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > offset = dfrag->offset + dfrag->data_len; > psize = pfrag->size - offset; > psize = min_t(size_t, psize, msg_data_left(msg)); > + psize = min_t(size_t, psize, copy_limit); Hi Paolo - Any concern that this will cause us to start sending short packets if mptcp_send_limit() starts returning small (nonzero) values? If copy_limit is small on the first iteration of this loop, it looks like a small segment will be created. When that gets acked, a small amount becomes available and then we create another small segment (repeat...). On the first pass (or on the 'wait_for_memory' path) should something like __mptcp_stream_is_writeable(sk, 1) be used to make sure a reasonable chunk of buffer is available before proceeding? Or is that the approach to this feature that got too complicated? :) - Mat > total_ts = psize + frag_truesize; > > if (!sk_wmem_schedule(sk, total_ts)) > @@ -3886,12 +3909,12 @@ static __poll_t mptcp_check_writeable(struct mptcp_sock *msk) > { > struct sock *sk = (struct sock *)msk; > > - if (sk_stream_is_writeable(sk)) > + if (__mptcp_stream_is_writeable(sk, 1)) > return EPOLLOUT | EPOLLWRNORM; > > set_bit(SOCK_NOSPACE, &sk->sk_socket->flags); > smp_mb__after_atomic(); /* NOSPACE is changed by mptcp_write_space() */ > - if (sk_stream_is_writeable(sk)) > + if (__mptcp_stream_is_writeable(sk, 1)) > return EPOLLOUT | EPOLLWRNORM; > > return 0; > diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h > index 3069d5c072b0..4a32d3d11fb6 100644 > --- a/net/mptcp/protocol.h > +++ b/net/mptcp/protocol.h > @@ -307,6 +307,7 @@ struct mptcp_sock { > in_accept_queue:1, > free_first:1, > rcvspace_init:1; > + u32 notsent_lowat; > struct work_struct work; > struct sk_buff *ooo_last_skb; > struct rb_root out_of_order_queue; > @@ -796,11 +797,36 @@ static inline bool mptcp_data_fin_enabled(const struct mptcp_sock *msk) > READ_ONCE(msk->write_seq) == READ_ONCE(msk->snd_nxt); > } > > +static inline u32 mptcp_notsent_lowat(const struct sock *sk) > +{ > + struct net *net = sock_net(sk); > + u32 val; > + > + val = READ_ONCE(mptcp_sk(sk)->notsent_lowat); > + return val ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat); > +} > + > +static inline bool __mptcp_stream_memory_free(const struct sock *sk, int wake) > +{ > + const struct mptcp_sock *msk = mptcp_sk(sk); > + u32 notsent_bytes; > + > + notsent_bytes = READ_ONCE(msk->write_seq) - READ_ONCE(msk->snd_nxt); > + return (notsent_bytes << wake) < mptcp_notsent_lowat(sk); > +} > + > +static inline bool __mptcp_stream_is_writeable(const struct sock *sk, int wake) > +{ > + return __mptcp_stream_memory_free(sk, wake) && > + __sk_stream_is_writeable(sk, wake); > +} > + > static inline void mptcp_write_space(struct sock *sk) > { > /* pairs with memory barrier in mptcp_poll */ > smp_mb(); > - sk_stream_write_space(sk); > + if (__mptcp_stream_memory_free(sk, 1)) > + sk_stream_write_space(sk); > } > > static inline void __mptcp_sync_sndbuf(struct sock *sk) > diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c > index ac37f6c5e2ed..1b38dac70719 100644 > --- a/net/mptcp/sockopt.c > +++ b/net/mptcp/sockopt.c > @@ -812,6 +812,16 @@ static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname, > return 0; > case TCP_ULP: > return -EOPNOTSUPP; > + case TCP_NOTSENT_LOWAT: > + ret = mptcp_get_int_option(msk, optval, optlen, &val); > + if (ret) > + return ret; > + > + lock_sock(sk); > + WRITE_ONCE(msk->notsent_lowat, val); > + mptcp_write_space(sk); > + release_sock(sk); > + return 0; > case TCP_CONGESTION: > return mptcp_setsockopt_sol_tcp_congestion(msk, optval, optlen); > case TCP_CORK: > @@ -1345,6 +1355,8 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname, > return mptcp_put_int_option(msk, optval, optlen, msk->cork); > case TCP_NODELAY: > return mptcp_put_int_option(msk, optval, optlen, msk->nodelay); > + case TCP_NOTSENT_LOWAT: > + return mptcp_put_int_option(msk, optval, optlen, msk->notsent_lowat); > } > return -EOPNOTSUPP; > } > -- > 2.43.0 > > >
On Wed, 2024-02-07 at 18:12 -0800, Mat Martineau wrote: > On Mon, 22 Jan 2024, Paolo Abeni wrote: > > > Add support for such socket option storing the user-space provided > > value in a new msk field, and using such data to implement the > > _mptcp_stream_memory_free() helper, similar to the TCP one. > > > > To avoid adding more indirect calls in the fast path, instead of > > hooking the new helper via the sk_stream_memory_free sock cb, > > add the directly calls where needed. > > > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/464 > > Signed-off-by: Paolo Abeni <pabeni@redhat.com> > > --- > > net/mptcp/protocol.c | 33 ++++++++++++++++++++++++++++----- > > net/mptcp/protocol.h | 28 +++++++++++++++++++++++++++- > > net/mptcp/sockopt.c | 12 ++++++++++++ > > 3 files changed, 67 insertions(+), 6 deletions(-) > > > > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c > > index 3599205fdceb..53d6c5544900 100644 > > --- a/net/mptcp/protocol.c > > +++ b/net/mptcp/protocol.c > > @@ -1761,6 +1761,25 @@ static int do_copy_data_nocache(struct sock *sk, int copy, > > return 0; > > } > > > > +static u32 mptcp_send_limit(const struct sock *sk) > > +{ > > + const struct mptcp_sock *msk = mptcp_sk(sk); > > + u32 limit, not_sent; > > + > > + if (!sk_stream_memory_free(sk)) > > + return 0; > > + > > + limit = mptcp_notsent_lowat(sk); > > + if (limit == UINT_MAX) > > + return UINT_MAX; > > + > > + not_sent = msk->write_seq - msk->snd_nxt; > > + if (not_sent >= limit) > > + return 0; > > + > > + return limit - not_sent; > > +} > > + > > static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > > { > > struct mptcp_sock *msk = mptcp_sk(sk); > > @@ -1805,6 +1824,12 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > > struct mptcp_data_frag *dfrag; > > bool dfrag_collapsed; > > size_t psize, offset; > > + u32 copy_limit; > > + > > + /* ensure fitting the notsent_lowat() constraint */ > > + copy_limit = mptcp_send_limit(sk); > > + if (!copy_limit) > > + goto wait_for_memory; > > > > /* reuse tail pfrag, if possible, or carve a new one from the > > * page allocator > > @@ -1812,9 +1837,6 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > > dfrag = mptcp_pending_tail(sk); > > dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag); > > if (!dfrag_collapsed) { > > - if (!sk_stream_memory_free(sk)) > > - goto wait_for_memory; > > - > > if (!mptcp_page_frag_refill(sk, pfrag)) > > goto wait_for_memory; > > > > @@ -1829,6 +1851,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > > offset = dfrag->offset + dfrag->data_len; > > psize = pfrag->size - offset; > > psize = min_t(size_t, psize, msg_data_left(msg)); > > + psize = min_t(size_t, psize, copy_limit); > > > Hi Paolo - > > Any concern that this will cause us to start sending short packets if > mptcp_send_limit() starts returning small (nonzero) values? > > If copy_limit is small on the first iteration of this loop, it looks like > a small segment will be created. When that gets acked, a small amount > becomes available and then we create another small segment (repeat...). The idea is to align the mptcp behavior with the one exposed by plain TCP. Note that wait_for_memory/sk_stream_wait_memory() should be woken-up only after __mptcp_stream_memory_free(sk, 1), see mptcp_write_space() below... > On the first pass (or on the 'wait_for_memory' path) should something like > __mptcp_stream_is_writeable(sk, 1) be used to make sure a reasonable chunk > of buffer is available before proceeding? ... so the above should be already guaranteed (and plain TCP does not check for that in tcp_sendmsg_locked/wait_for_space. Anyway I think you outlined a bug here: mptcp_sendmsg() waits for mptcp_notsent_lowat/__mptcp_stream_memory_free(sk, 0) but I explicitly avoided to set sk_prot->stream_memory_free, so sk_stream_wait_memory() could wake the reader too early. I'll send a v2 addressing the above. Cheers, Paolo
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 3599205fdceb..53d6c5544900 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1761,6 +1761,25 @@ static int do_copy_data_nocache(struct sock *sk, int copy, return 0; } +static u32 mptcp_send_limit(const struct sock *sk) +{ + const struct mptcp_sock *msk = mptcp_sk(sk); + u32 limit, not_sent; + + if (!sk_stream_memory_free(sk)) + return 0; + + limit = mptcp_notsent_lowat(sk); + if (limit == UINT_MAX) + return UINT_MAX; + + not_sent = msk->write_seq - msk->snd_nxt; + if (not_sent >= limit) + return 0; + + return limit - not_sent; +} + static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) { struct mptcp_sock *msk = mptcp_sk(sk); @@ -1805,6 +1824,12 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) struct mptcp_data_frag *dfrag; bool dfrag_collapsed; size_t psize, offset; + u32 copy_limit; + + /* ensure fitting the notsent_lowat() constraint */ + copy_limit = mptcp_send_limit(sk); + if (!copy_limit) + goto wait_for_memory; /* reuse tail pfrag, if possible, or carve a new one from the * page allocator @@ -1812,9 +1837,6 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) dfrag = mptcp_pending_tail(sk); dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag); if (!dfrag_collapsed) { - if (!sk_stream_memory_free(sk)) - goto wait_for_memory; - if (!mptcp_page_frag_refill(sk, pfrag)) goto wait_for_memory; @@ -1829,6 +1851,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) offset = dfrag->offset + dfrag->data_len; psize = pfrag->size - offset; psize = min_t(size_t, psize, msg_data_left(msg)); + psize = min_t(size_t, psize, copy_limit); total_ts = psize + frag_truesize; if (!sk_wmem_schedule(sk, total_ts)) @@ -3886,12 +3909,12 @@ static __poll_t mptcp_check_writeable(struct mptcp_sock *msk) { struct sock *sk = (struct sock *)msk; - if (sk_stream_is_writeable(sk)) + if (__mptcp_stream_is_writeable(sk, 1)) return EPOLLOUT | EPOLLWRNORM; set_bit(SOCK_NOSPACE, &sk->sk_socket->flags); smp_mb__after_atomic(); /* NOSPACE is changed by mptcp_write_space() */ - if (sk_stream_is_writeable(sk)) + if (__mptcp_stream_is_writeable(sk, 1)) return EPOLLOUT | EPOLLWRNORM; return 0; diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 3069d5c072b0..4a32d3d11fb6 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -307,6 +307,7 @@ struct mptcp_sock { in_accept_queue:1, free_first:1, rcvspace_init:1; + u32 notsent_lowat; struct work_struct work; struct sk_buff *ooo_last_skb; struct rb_root out_of_order_queue; @@ -796,11 +797,36 @@ static inline bool mptcp_data_fin_enabled(const struct mptcp_sock *msk) READ_ONCE(msk->write_seq) == READ_ONCE(msk->snd_nxt); } +static inline u32 mptcp_notsent_lowat(const struct sock *sk) +{ + struct net *net = sock_net(sk); + u32 val; + + val = READ_ONCE(mptcp_sk(sk)->notsent_lowat); + return val ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat); +} + +static inline bool __mptcp_stream_memory_free(const struct sock *sk, int wake) +{ + const struct mptcp_sock *msk = mptcp_sk(sk); + u32 notsent_bytes; + + notsent_bytes = READ_ONCE(msk->write_seq) - READ_ONCE(msk->snd_nxt); + return (notsent_bytes << wake) < mptcp_notsent_lowat(sk); +} + +static inline bool __mptcp_stream_is_writeable(const struct sock *sk, int wake) +{ + return __mptcp_stream_memory_free(sk, wake) && + __sk_stream_is_writeable(sk, wake); +} + static inline void mptcp_write_space(struct sock *sk) { /* pairs with memory barrier in mptcp_poll */ smp_mb(); - sk_stream_write_space(sk); + if (__mptcp_stream_memory_free(sk, 1)) + sk_stream_write_space(sk); } static inline void __mptcp_sync_sndbuf(struct sock *sk) diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c index ac37f6c5e2ed..1b38dac70719 100644 --- a/net/mptcp/sockopt.c +++ b/net/mptcp/sockopt.c @@ -812,6 +812,16 @@ static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname, return 0; case TCP_ULP: return -EOPNOTSUPP; + case TCP_NOTSENT_LOWAT: + ret = mptcp_get_int_option(msk, optval, optlen, &val); + if (ret) + return ret; + + lock_sock(sk); + WRITE_ONCE(msk->notsent_lowat, val); + mptcp_write_space(sk); + release_sock(sk); + return 0; case TCP_CONGESTION: return mptcp_setsockopt_sol_tcp_congestion(msk, optval, optlen); case TCP_CORK: @@ -1345,6 +1355,8 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname, return mptcp_put_int_option(msk, optval, optlen, msk->cork); case TCP_NODELAY: return mptcp_put_int_option(msk, optval, optlen, msk->nodelay); + case TCP_NOTSENT_LOWAT: + return mptcp_put_int_option(msk, optval, optlen, msk->notsent_lowat); } return -EOPNOTSUPP; }
Add support for such socket option storing the user-space provided value in a new msk field, and using such data to implement the _mptcp_stream_memory_free() helper, similar to the TCP one. To avoid adding more indirect calls in the fast path, instead of hooking the new helper via the sk_stream_memory_free sock cb, add the directly calls where needed. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/464 Signed-off-by: Paolo Abeni <pabeni@redhat.com> --- net/mptcp/protocol.c | 33 ++++++++++++++++++++++++++++----- net/mptcp/protocol.h | 28 +++++++++++++++++++++++++++- net/mptcp/sockopt.c | 12 ++++++++++++ 3 files changed, 67 insertions(+), 6 deletions(-)