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Re: [PATCH] tcp: add window scaling support


From: Josef Bacik
Subject: Re: [PATCH] tcp: add window scaling support
Date: Tue, 18 Aug 2015 10:48:20 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 08/17/2015 09:15 AM, Andrei Borzenkov wrote:
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.

Ok I'll add a config option.


Signed-off-by: Josef Bacik <address@hidden>
---
  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.

Fair enough.


  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.

So I only care about connections we open, not about connections that are opened to us which is why I did it this way. If we start to care about how fast grub can transfer stuff _to_ somebody else we can add it there as well. Thanks,

Josef



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