netdev - Re: [PATCH net-next v2 4/4] bonding: balance ICMP echoes in layer3+4 mode

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Date:   Tue, 29 Oct 2019 16:04:43 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Matteo Croce <mcroce@...hat.com>, netdev@...r.kernel.org
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller" <davem@...emloft.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Paul Blakey <paulb@...lanox.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 4/4] bonding: balance ICMP echoes in layer3+4
 mode



On 10/29/19 2:50 PM, Nikolay Aleksandrov wrote:

> Right, I was just giving it as an example. Your suggestion sounds much better and
> wouldn't interfere with other layers, plus we already use skb->hash in bond_xmit_hash()
> and skb_set_owner_w() sets l4_hash if txhash is present which is perfect.
> 
> One thing - how do we deal with sk_rethink_txhash() ? I guess we'll need some way to
> signal that the user specified the txhash and it is not to be recomputed ?
> That can also be used to avoid the connect txhash set as well if SO_TXHASH was set prior
> to the connect. It's quite late here, I'll look into it more tomorrow. :)

I guess that we have something similar with SO_RCVBUF/SO_SNDBUF

autotuning is disabled when/if they are used :

 SOCK_RCVBUF_LOCK & SOCK_SNDBUF_LOCK

We could add a SOCK_TXHASH_LOCK so that sk_rethink_txhash() does nothing if
user forced a TXHASH value.

Something like the following (probably not complete) patch.

diff --git a/include/net/sock.h b/include/net/sock.h
index 380312cc67a9d9ee8720eb2db82b1f7f8a5615ab..a8882738710eaa9d9d629e1207837a798401a594 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1354,6 +1354,7 @@ static inline int __sk_prot_rehash(struct sock *sk)
 #define SOCK_RCVBUF_LOCK       2
 #define SOCK_BINDADDR_LOCK     4
 #define SOCK_BINDPORT_LOCK     8
+#define SOCK_TXHASH_LOCK       16
 
 struct socket_alloc {
        struct socket socket;
@@ -1852,7 +1853,8 @@ static inline u32 net_tx_rndhash(void)
 
 static inline void sk_set_txhash(struct sock *sk)
 {
-       sk->sk_txhash = net_tx_rndhash();
+       if (!(sk->sk_userlocks & SOCK_TXHASH_LOCK))
+               sk->sk_txhash = net_tx_rndhash();
 }
 
 static inline void sk_rethink_txhash(struct sock *sk)
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 77f7c1638eb1ce7d3e143bbffd60056e472b1122..998be6ee7991de3a76d4ad33df3a38dbe791eae8 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -118,6 +118,7 @@
 #define SO_SNDTIMEO_NEW         67
 
 #define SO_DETACH_REUSEPORT_BPF 68
+#define SO_TXHASH              69
 
 #if !defined(__KERNEL__)
 
diff --git a/net/core/sock.c b/net/core/sock.c
index 997b352c2a72ee39f00b102a553ac1191202b74f..85b85dffd462bc3b497e0432100ff24b759832e0 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -770,6 +770,10 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
        case SO_BROADCAST:
                sock_valbool_flag(sk, SOCK_BROADCAST, valbool);
                break;
+       case SO_TXHASH:
+               sk->sk_txhash = val;
+               sk->sk_userlocks |= SOCK_TXHASH_LOCK;
+               break;
        case SO_SNDBUF:
                /* Don't error on this BSD doesn't and if you think
                 * about it this is right. Otherwise apps have to
@@ -1249,6 +1253,10 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
                v.val = sock_flag(sk, SOCK_BROADCAST);
                break;
 
+       case SO_TXHASH:
+               v.val = sk->sk_txhash;
+               break;
+
        case SO_SNDBUF:
                v.val = sk->sk_sndbuf;
                break;