Re: [PATCH] tcp: add window scaling support

[Andrei Borzenkov <arvidjaar@gmail.com>]

12.08.2015 18:57, Josef Bacik пишет:
> Sometimes we have to provision boxes across regions, such as California to
> Sweden.  The http server has a 10 minute timeout, so if we can't get our 250mb
> image transferred fast enough our provisioning fails, which is not ideal.  So
> add tcp window scaling on open connections and set the window size to 1mb.  With
> this change we're able to get higher sustained transfers between regions and can
> transfer our image in well below 10 minutes.  Without this patch we'd time out
> every time halfway through the transfer.  Thanks,
>

I do not think having 1M TCP window by default is good idea. We probably 
could make it configurable if there are evidences that it is really 
required.

> Signed-off-by: Josef Bacik <jbacik@fb.com>
> ---
>   grub-core/net/tcp.c | 42 +++++++++++++++++++++++++++++-------------
>   1 file changed, 29 insertions(+), 13 deletions(-)
>
> diff --git a/grub-core/net/tcp.c b/grub-core/net/tcp.c
> index 5da8b11..57a6d4e 100644
> --- a/grub-core/net/tcp.c
> +++ b/grub-core/net/tcp.c
> @@ -106,6 +106,18 @@ struct tcphdr
>     grub_uint16_t urgent;
>   } GRUB_PACKED;
>
> +struct tcp_scale_opt {
> +  grub_uint8_t kind;
> +  grub_uint8_t length;
> +  grub_uint8_t scale;
> +} GRUB_PACKED;
> +
> +struct tcp_synhdr {
> +  struct tcphdr tcphdr;
> +  struct tcp_scale_opt scale_opt;
> +  grub_uint8_t padding;
> +};
> +

No, this does not scale. Just allocate large enough buffer and use 
pointers inside it. We may want to support multiple options at some point.

>   struct tcp_pseudohdr
>   {
>     grub_uint32_t src;
> @@ -555,7 +567,7 @@ grub_net_tcp_open (char *server,
>     grub_net_tcp_socket_t socket;
>     static grub_uint16_t in_port = 21550;
>     struct grub_net_buff *nb;
> -  struct tcphdr *tcph;
> +  struct tcp_synhdr *tcph;
>     int i;
>     grub_uint8_t *nbd;
>     grub_net_link_level_address_t ll_target_addr;
> @@ -617,20 +629,24 @@ grub_net_tcp_open (char *server,
>       }
>
>     tcph = (void *) nb->data;
> +  grub_memset(tcph, 0, sizeof (*tcph));
>     socket->my_start_seq = grub_get_time_ms ();
>     socket->my_cur_seq = socket->my_start_seq + 1;
> -  socket->my_window = 8192;
> -  tcph->seqnr = grub_cpu_to_be32 (socket->my_start_seq);
> -  tcph->ack = grub_cpu_to_be32_compile_time (0);
> -  tcph->flags = grub_cpu_to_be16_compile_time ((5 << 12) | TCP_SYN);
> -  tcph->window = grub_cpu_to_be16 (socket->my_window);
> -  tcph->urgent = 0;
> -  tcph->src = grub_cpu_to_be16 (socket->in_port);
> -  tcph->dst = grub_cpu_to_be16 (socket->out_port);
> -  tcph->checksum = 0;
> -  tcph->checksum = grub_net_ip_transport_checksum (nb, GRUB_NET_IP_TCP,
> -						   &socket->inf->address,
> -						   &socket->out_nla);
> +  socket->my_window = 32768;
> +  tcph->tcphdr.seqnr = grub_cpu_to_be32 (socket->my_start_seq);
> +  tcph->tcphdr.ack = grub_cpu_to_be32_compile_time (0);
> +  tcph->tcphdr.flags = grub_cpu_to_be16_compile_time ((6 << 12) | TCP_SYN);
> +  tcph->tcphdr.window = grub_cpu_to_be16 (socket->my_window);
> +  tcph->tcphdr.urgent = 0;
> +  tcph->tcphdr.src = grub_cpu_to_be16 (socket->in_port);
> +  tcph->tcphdr.dst = grub_cpu_to_be16 (socket->out_port);
> +  tcph->tcphdr.checksum = 0;
> +  tcph->scale_opt.kind = 3;
> +  tcph->scale_opt.length = 3;
> +  tcph->scale_opt.scale = 5;
> +  tcph->tcphdr.checksum = grub_net_ip_transport_checksum (nb, GRUB_NET_IP_TCP,
> +							  &socket->inf->address,
> +							  &socket->out_nla);
>
>     tcp_socket_register (socket);
>
>

There is one more place - grub_net_tcp_accept. Not sure if it ever be 
used though.