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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> ==== 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]]
