netdev - Re: [RFC, RESEND] UDP receive path batching improvement

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Message-ID: <CANn89iJ-Xqb2uOZwyatq-6gMHPVt0xga_dypiF_X8Z_L0eao4w@mail.gmail.com>
Date: Fri, 22 Aug 2025 06:20:25 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Balazs Scheidler <bazsi77@...il.com>
Cc: netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [RFC, RESEND] UDP receive path batching improvement

On Fri, Aug 22, 2025 at 6:10 AM Eric Dumazet <edumazet@...gle.com> wrote:
>

>
> Can you post
>
> ss -aum src :1000  <replace 1000 with your UDP source port>
>
> We will check the dXXXX output (number of drops), per socket.

Small experiment :

otrv5:/home/edumazet# ./super_netperf 10 -t UDP_STREAM -H otrv6 -l10
-- -n -P,1000 -m 1200
   4304

If I remove the problematic sk_drops update :

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index efd742279289fc13aec9369d0f01a3be3aa73151..8976399d4e52f21058f74fde13d46e35c7617deb
100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1575,7 +1575,8 @@ int __udp_enqueue_schedule_skb(struct sock *sk,
struct sk_buff *skb)
        atomic_sub(skb->truesize, &sk->sk_rmem_alloc);

 drop:
-       atomic_inc(&sk->sk_drops);
+// Find a better way to make this operation not too expensive.
+//     atomic_inc(&sk->sk_drops);
        busylock_release(busy);
        return err;
 }

otrv5:/home/edumazet# ./super_netperf 10 -t UDP_STREAM -H otrv6 -l10
-- -n -P,1000 -m 1200
   6076

So there is definitely room for a big improvement here.