Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as drain mode
From: Eric Dumazet <hidden>
Date: 2016-03-24 16:33:13
On Thu, 2016-03-24 at 16:30 +0100, Willy Tarreau wrote:
quoted hunk ↗ jump to hunk
Hi Eric, (just lost my e-mail, trying not to forget some points) On Thu, Mar 24, 2016 at 07:45:44AM -0700, Eric Dumazet wrote:quoted
On Thu, 2016-03-24 at 15:22 +0100, Willy Tarreau wrote:quoted
Hi Eric,quoted
But that means that any software making use of SO_REUSEPORT needs to also implement BPF on Linux to achieve the same as what it does on other OSes ? Also I found a case where a dying process would still cause trouble in the accept queue, maybe it's not redistributed, I don't remember, all I remember is that my traffic stopped after a segfault of only one of them :-/ I'll have to dig a bit regarding this.Hi Willy Problem is : If we add a SO_REUSEPORT_LISTEN_OFF, this wont work with BPF.I wasn't for adding SO_REUSEPORT_LISTEN_OFF either. Instead the idea was just to modify the score in compute_score() so that a socket which disables SO_REUSEPORT scores less than one which still has it. The application wishing to terminate just has to clear the SO_REUSEPORT flag and wait for accept() reporting EAGAIN. The patch simply looked like this (copy-pasted hence space-mangled) :--- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c@@ -189,6 +189,8 @@ static inline int compute_score(struct sock *sk, struct net *net, return -1; score += 4; } + if (sk->sk_reuseport) + score++;
This wont work with BPF
if (sk->sk_incoming_cpu == raw_smp_processor_id())
score++;This one does not work either with BPF
}quoted
BPF makes a decision without knowing individual listeners states.But is the decision taken without considering compute_score() ? The point really was to be the least possibly intrusive and quite logical for the application : "disable SO_REUSEPORT when you don't want to participate to incoming load balancing anymore".
Whole point of BPF was to avoid iterate through all sockets [1], and let user space use whatever selection logic it needs. [1] This was okay with up to 16 sockets. But with 128 it does not scale. If you really look at how BPF works, implementing another 'per listener' flag would break the BPF selection. You can certainly implement the SO_REUSEPORT_LISTEN_OFF by loading an updated BPF, why should we add another way in the kernel to do the same, in a way that would not work in some cases ?