netdev - Re: [RFC PATCH 3/4] udp: implement GRO plain UDP sockets.

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Message-ID: <1e140072-15f6-755c-28be-61534b243d62@gmail.com>
Date:   Fri, 14 Sep 2018 09:48:11 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [RFC PATCH 3/4] udp: implement GRO plain UDP sockets.



On 09/14/2018 08:43 AM, Paolo Abeni wrote:
> This is the RX counter part of commit bec1f6f69736 ("udp: generate gso
> with UDP_SEGMENT"). When UDP_SEGMENT is enabled, such socket is also
> eligible for GRO in the rx path: UDP segments directed to such socket
> are assembled into a larger GSO_UDP_L4 packet.
> 
> The core UDP GRO support is enabled/updated on setsockopt(UDP_SEGMENT) and
> disabled, if needed at socket destruction time.
> 
> Initial benchmark numbers:
> 
> Before:
> udp rx:   1079 MB/s   769065 calls/s
> 
> After:
> udp rx:   1466 MB/s    24877 calls/s


Are you sure the data is actually fully copied to user space ?

tools/testing/selftests/net/udpgso_bench_rx.c

uses :

static char rbuf[ETH_DATA_LEN];
   /* MSG_TRUNC will make return value full datagram length */
   ret = recv(fd, rbuf, len, MSG_TRUNC | MSG_DONTWAIT);

So you need to change this program.

Also, GRO reception would mean that userspace can retrieve,
not only full bytes of X datagrams, but also the gso_size (or length of individual datagrams)

You can not know the size of the packets in advance, the sender will decide.