Re: [PATCH v2 for 8.0?] nbd/server: Request TCP_NODELAY

[Paolo Bonzini <pbonzini@redhat.com>]

On 4/4/23 02:40, Eric Blake wrote:
> Nagle's algorithm adds latency in order to reduce network packet
> overhead on small packets.  But when we are already using corking to
> merge smaller packets into transactional requests, the extra delay
> from TCP defaults just gets in the way (see recent commit bd2cd4a4).
> 
> For reference, qemu as an NBD client already requests TCP_NODELAY (see
> nbd_connect() in nbd/client-connection.c); as does libnbd as a client
> [1], and nbdkit as a server [2].  Furthermore, the NBD spec recommends
> the use of TCP_NODELAY [3].
> 
> [1] https://gitlab.com/nbdkit/libnbd/-/blob/a48a1142/generator/states-connect.c#L39
> [2] https://gitlab.com/nbdkit/nbdkit/-/blob/45b72f5b/server/sockets.c#L430
> [3] https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md#protocol-phases
> 
> CC: Florian Westphal <fw@strlen.de>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> Message-Id: <20230327192947.1324372-1-eblake@redhat.com>
> ---
> 
> v2 fix typo, enhance commit message
> 
> Given that corking made it in through Kevin's tree for 8.0-rc2 but
> this one did not, but I didn't get any R-b, is there any objection to
> me doing a pull request to get this into 8.0-rc3?
> 
>   nbd/server.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/nbd/server.c b/nbd/server.c
> index 848836d4140..3d8d0d81df2 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -2758,6 +2758,7 @@ void nbd_client_new(QIOChannelSocket *sioc,
>       }
>       client->tlsauthz = g_strdup(tlsauthz);
>       client->sioc = sioc;
> +    qio_channel_set_delay(QIO_CHANNEL(sioc), false);
>       object_ref(OBJECT(client->sioc));
>       client->ioc = QIO_CHANNEL(sioc);
>       object_ref(OBJECT(client->ioc));
> 
> base-commit: efcd0ec14b0fe9ee0ee70277763b2d538d19238d

Acked-by: Paolo Bonzini <pbonzini@redhat.com>