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Message-ID: <20231215015807.39107-1-kuniyu@amazon.com>
Date: Fri, 15 Dec 2023 10:58:07 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <jakub@...udflare.com>,
<kuba@...nel.org>, <netdev@...r.kernel.org>, <pabeni@...hat.com>, "Kuniyuki
Iwashima" <kuniyu@...zon.com>
Subject: [PATCH net-next 2/2] tcp/dccp: change source port selection at connect() time
From: Eric Dumazet <edumazet@...gle.com>
Date: Thu, 14 Dec 2023 19:29:39 +0000
> In commit 1580ab63fc9a ("tcp/dccp: better use of ephemeral ports in connect()")
> we added an heuristic to select even ports for connect() and odd ports for bind().
>
> This was nice because no applications changes were needed.
>
> But it added more costs when all even ports are in use,
> when there are few listeners and many active connections.
>
> Since then, IP_LOCAL_PORT_RANGE has been added to permit an application
> to partition ephemeral port range at will.
>
> This patch extends the idea so that if IP_LOCAL_PORT_RANGE is set on
> a socket before accept(), port selection no longer favors even ports.
>
> This means that connect() can find a suitable source port faster,
> and applications can use a different split between connect() and bind()
> users.
>
> This should give more entropy to Toeplitz hash used in RSS: Using even
> ports was wasting one bit from the 16bit sport.
>
> A similar change can be done in inet_csk_find_open_port() if needed.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> Cc: Jakub Sitnicki <jakub@...udflare.com>
> ---
> net/ipv4/inet_hashtables.c | 27 ++++++++++++++++-----------
> 1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index a532f749e47781cc951f2003f621cec4387a2384..9ff201bc4e6d2da04735e8c160d446602e0adde1 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -1012,7 +1012,8 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
> bool tb_created = false;
> u32 remaining, offset;
> int ret, i, low, high;
> - int l3mdev;
> + bool local_ports;
> + int step, l3mdev;
> u32 index;
>
> if (port) {
> @@ -1024,10 +1025,12 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
>
> l3mdev = inet_sk_bound_l3mdev(sk);
>
> - inet_sk_get_local_port_range(sk, &low, &high);
> + local_ports = inet_sk_get_local_port_range(sk, &low, &high);
> + step = local_ports ? 1 : 2;
> +
> high++; /* [32768, 60999] -> [32768, 61000[ */
> remaining = high - low;
> - if (likely(remaining > 1))
> + if (!local_ports && remaining > 1)
> remaining &= ~1U;
>
> get_random_sleepable_once(table_perturb,
> @@ -1040,10 +1043,11 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
> /* In first pass we try ports of @low parity.
> * inet_csk_get_port() does the opposite choice.
> */
> - offset &= ~1U;
> + if (!local_ports)
> + offset &= ~1U;
> other_parity_scan:
> port = low + offset;
> - for (i = 0; i < remaining; i += 2, port += 2) {
> + for (i = 0; i < remaining; i += step, port += step) {
> if (unlikely(port >= high))
> port -= remaining;
> if (inet_is_local_reserved_port(net, port))
> @@ -1083,10 +1087,11 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
> cond_resched();
> }
>
> - offset++;
> - if ((offset & 1) && remaining > 1)
> - goto other_parity_scan;
> -
> + if (!local_ports) {
> + offset++;
> + if ((offset & 1) && remaining > 1)
> + goto other_parity_scan;
> + }
> return -EADDRNOTAVAIL;
>
> ok:
> @@ -1109,8 +1114,8 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
> * on low contention the randomness is maximal and on high contention
> * it may be inexistent.
> */
> - i = max_t(int, i, get_random_u32_below(8) * 2);
> - WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + 2);
> + i = max_t(int, i, get_random_u32_below(8) * step);
> + WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + step);
>
> /* Head lock still held and bh's disabled */
> inet_bind_hash(sk, tb, tb2, port);
> --
> 2.43.0.472.g3155946c3a-goog
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