From 92ac8acc01f9152947140fd012f503c382c67b75 Mon Sep 17 00:00:00 2001 From: Thierry Reding Date: Tue, 19 Aug 2014 10:21:24 +0200 Subject: [PATCH] net: More BOOTP retry timeout improvements It's not unusual for DHCP servers to take a couple hundred milliseconds to respond to DHCP discover messages. One possible reason for the delay can be that the server checks (typically using an ARP request) that the IP it's about to hand out isn't in use yet. To make matters worse, some servers may also queue up requests and process them sequentially, which can cause excessively long delays if clients retry too fast. Commit f59be6e850b3 ("net: BOOTP retry timeout improvements") shortened the retry timeouts significantly, but the BOOTP/DHCP implementation in U-Boot doesn't handle that well because it will ignore incoming replies to earlier requests. In one particular setup this increases the time it takes to obtain a DHCP lease from 630 ms to 8313 ms. This commit attempts to fix this in two ways. First it increases the initial retry timeout from 10 ms to 250 ms to give DHCP servers some more time to respond. At the same time a cache of outstanding DHCP request IDs is kept so that the implementation will know to continue transactions even after a retransmission of the DISCOVER message. The maximum retry timeout is also increased from 1 second to 2 seconds. An ID cache of size 4 will keep DHCP requests around for 8 seconds (once the maximum retry timeout has been reached) before dropping them. This should give servers plenty of time to respond. If it ever turns out that this isn't enough, the size of the cache can easily be increased. With this commit the DHCP lease on the above-mentioned setup still takes longer (1230 ms) than originally, but that's an acceptable compromise to improve DHCP lease acquisition time for a broader range of setups. To make it easier to benchmark DHCP in the future, this commit also adds the time it took to obtain a lease to the final "DHCP client bound to address x.x.x.x" message. Tested-by: Stephen Warren Signed-off-by: Thierry Reding --- README | 18 ++++++++++++++++++ net/bootp.c | 48 ++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 58 insertions(+), 8 deletions(-) diff --git a/README b/README index 1d713596ec..d1b4eed020 100644 --- a/README +++ b/README @@ -2036,6 +2036,24 @@ CBFS (Coreboot Filesystem) support 4th and following BOOTP requests: delay 0 ... 8 sec + CONFIG_BOOTP_ID_CACHE_SIZE + + BOOTP packets are uniquely identified using a 32-bit ID. The + server will copy the ID from client requests to responses and + U-Boot will use this to determine if it is the destination of + an incoming response. Some servers will check that addresses + aren't in use before handing them out (usually using an ARP + ping) and therefore take up to a few hundred milliseconds to + respond. Network congestion may also influence the time it + takes for a response to make it back to the client. If that + time is too long, U-Boot will retransmit requests. In order + to allow earlier responses to still be accepted after these + retransmissions, U-Boot's BOOTP client keeps a small cache of + IDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of this + cache. The default is to keep IDs for up to four outstanding + requests. Increasing this will allow U-Boot to accept offers + from a BOOTP client in networks with unusually high latency. + - DHCP Advanced Options: You can fine tune the DHCP functionality by defining CONFIG_BOOTP_* symbols: diff --git a/net/bootp.c b/net/bootp.c index a4f6db570c..d4c86cf179 100644 --- a/net/bootp.c +++ b/net/bootp.c @@ -47,7 +47,12 @@ #define CONFIG_DHCP_MIN_EXT_LEN 64 #endif -ulong BootpID; +#ifndef CONFIG_BOOTP_ID_CACHE_SIZE +#define CONFIG_BOOTP_ID_CACHE_SIZE 4 +#endif + +ulong bootp_ids[CONFIG_BOOTP_ID_CACHE_SIZE]; +unsigned int bootp_num_ids; int BootpTry; ulong bootp_start; ulong bootp_timeout; @@ -77,6 +82,30 @@ static char *dhcpmsg2str(int type) #endif #endif +static void bootp_add_id(ulong id) +{ + if (bootp_num_ids >= ARRAY_SIZE(bootp_ids)) { + size_t size = sizeof(bootp_ids) - sizeof(id); + + memmove(bootp_ids, &bootp_ids[1], size); + bootp_ids[bootp_num_ids - 1] = id; + } else { + bootp_ids[bootp_num_ids] = id; + bootp_num_ids++; + } +} + +static bool bootp_match_id(ulong id) +{ + unsigned int i; + + for (i = 0; i < bootp_num_ids; i++) + if (bootp_ids[i] == id) + return true; + + return false; +} + static int BootpCheckPkt(uchar *pkt, unsigned dest, unsigned src, unsigned len) { struct Bootp_t *bp = (struct Bootp_t *) pkt; @@ -96,7 +125,7 @@ static int BootpCheckPkt(uchar *pkt, unsigned dest, unsigned src, unsigned len) retval = -4; else if (bp->bp_hlen != HWL_ETHER) retval = -5; - else if (NetReadLong((ulong *)&bp->bp_id) != BootpID) + else if (!bootp_match_id(NetReadLong((ulong *)&bp->bp_id))) retval = -6; debug("Filtering pkt = %d\n", retval); @@ -351,8 +380,8 @@ BootpTimeout(void) #endif } else { bootp_timeout *= 2; - if (bootp_timeout > 1000) - bootp_timeout = 1000; + if (bootp_timeout > 2000) + bootp_timeout = 2000; NetSetTimeout(bootp_timeout, BootpTimeout); BootpRequest(); } @@ -616,9 +645,10 @@ static int BootpExtended(u8 *e) void BootpReset(void) { + bootp_num_ids = 0; BootpTry = 0; bootp_start = get_timer(0); - bootp_timeout = 10; + bootp_timeout = 250; } void @@ -631,6 +661,7 @@ BootpRequest(void) #ifdef CONFIG_BOOTP_RANDOM_DELAY ulong rand_ms; #endif + ulong BootpID; bootstage_mark_name(BOOTSTAGE_ID_BOOTP_START, "bootp_start"); #if defined(CONFIG_CMD_DHCP) @@ -699,7 +730,8 @@ BootpRequest(void) | ((ulong)NetOurEther[4] << 8) | (ulong)NetOurEther[5]; BootpID += get_timer(0); - BootpID = htonl(BootpID); + BootpID = htonl(BootpID); + bootp_add_id(BootpID); NetCopyLong(&bp->bp_id, &BootpID); /* @@ -960,8 +992,8 @@ DhcpHandler(uchar *pkt, unsigned dest, IPaddr_t sip, unsigned src, /* Store net params from reply */ BootpCopyNetParams(bp); dhcp_state = BOUND; - printf("DHCP client bound to address %pI4\n", - &NetOurIP); + printf("DHCP client bound to address %pI4 (%lu ms)\n", + &NetOurIP, get_timer(bootp_start)); bootstage_mark_name(BOOTSTAGE_ID_BOOTP_STOP, "bootp_stop"); -- 2.39.5