✎ soc:2010:cooldavid:journal:week2

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==== Week 2 [ 31 May - 6 Jun 2010 ]: Discuss TCP and memory changes, update jme driver ====
==== jme driver ====
  * From Joshua Oreman
    * jme_check_link(struct net_device *netdev, int testonly)\\
      * In this function, I believe the code and string data used in constructing linkmsg will make it into even non-debug versions of the executable. If that's true it would be better if you could perform all the manipulations in the final DBG() line, using the ?: operator and such. It's possible the compiler is clever enough to know what strcat() does and see that linkmsg[] is not used in non-debug, though, so this may be moot.
  * From Michael Brown
    * if (memcmp(addr, netdev->hw_addr, ETH_ALEN))
      * No need for this compare; just always write the MAC address.  (This code will fail if you set the MAC to a non-default value, then try to set it back.)
    * Code cleanups
      * gPXE dose not use any DMA address that is above 4G <code C>
#if __x86_64__
     rxdesc->desc1.flags     = RXFLAG_64BIT;
#endif
</code>
      * Use struct ethhdr and eth_ntoa().
      * Drivers should generally not try to parse the packets they transmit and receive.
      * This code will break if/when software VLAN support is added. <code C>
            DBG2("Received packet: "
                 "from %02x:%02x:%02x:%02x:%02x:%02x "
                 "to %02x:%02x:%02x:%02x:%02x:%02x "
                 "type %04x\n",
                 *(uint8_t *)(rxbi->data + 6),
                 *(uint8_t *)(rxbi->data + 7),
                 *(uint8_t *)(rxbi->data + 8),
                 *(uint8_t *)(rxbi->data + 9),
                 *(uint8_t *)(rxbi->data + 10),
                 *(uint8_t *)(rxbi->data + 11),
                 *(uint8_t *)(rxbi->data + 0),
                 *(uint8_t *)(rxbi->data + 1),
                 *(uint8_t *)(rxbi->data + 2),
                 *(uint8_t *)(rxbi->data + 3),
                 *(uint8_t *)(rxbi->data + 4),
                 *(uint8_t *)(rxbi->data + 5),
                 be16_to_cpu(*(uint16_t *)(rxbi->data + 12)));
</code>
      * %p should be used for printing out pointer values. <code C>
    DBG2("TX buffer address: %08lx(%08lx+%x)\n",
                    (unsigned long)iob->data, mapping, len);
</code>
    * This will behave poorly when memory runs out. Better is to have a refill routine that runs after the poll(), and always attempts to refill up to a specified level. <code C>
    rxdesc += idx;
    if (jme_make_new_rx_buf(rxring->bufinf + idx)) {
            DBG("Dropped packet due to memory allocation error.\n");
            netdev_rx_err(netdev, NULL, -ENOMEM);
    } else {
</code>

  * From me:
    * The refill function did not work correctly. Because of the error packet was reused instead of making a hole. [[http://bbs.cooldavid.org/git/?p=gpxe.git;a=commitdiff;h=aa105ed1c6d99588dceeec3ead4e434b40b59644|This patch fixed it]]

==== Trace memory related codes ====
  * Current heap size is fixed at 128K.
  * Trying to figure out a way to obtain more memory, and report it to OS.
  * See if it is possiable to know how much heap size we can use out of code and stack.

=== Schedule for memory and TCP modifications ===
  - Trace how the gPXE boot, relocate, and fill segment informations.
  - Try to understand how Michael Brown removes the even magabyte limit.
  - Start a discussion on the list about how to reasonably extend gPXE's usable memory.
  - Patch gPXE to support large(Several MB perhaps) heap memory.
  - Design/discuss a TCP receive window advertisement algorithm.
  - Patch gPXE with ''**TCP receive queue**'', ''**SACK Support**'', and ''**Window scale**''.
  - Do some benchmark against different window size, and different network environment.
  - Post the result and discuss it on the gpxe mailling-list.

=== Some notes after trace ===
  * [[soc:2010:cooldavid:notes:gpxememlayout|gPXE memory layout]]
  * Good articals for understanding Gate-A20
    - [[http://en.wikipedia.org/wiki/A20_line|WIKIPEDIA - A20 line]]
    - [[http://www.win.tue.nl/~aeb/linux/kbd/A20.html|A20 - a pain from the past]]

=== Expand heap ===
  * [[soc:2010:cooldavid:notes:expandheap|Expand gPXE heap]]

Trace: • iscsibootprepw2k3 • derekpryor-proposal • debian_and_ubuntu • ideas • project_plan • stefanha • irc_logs_for_e820_issue • info • week8 • yazzy • debian_lenny_iscsi • gpxeonqemu091 • notes • willem • dverkamp • 2009 • howtos • 2006 • mdc_sandbox • audit-the-shifts