[U-Boot] [U-Boot, v2] net: More BOOTP retry timeout improvements

[Tom Rini]

On Tue, Aug 19, 2014 at 10:21:24AM +0200, Thierry Reding wrote:

> From: Thierry Reding <treding at nvidia.com>
> 
> 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 <swarren at nvidia.com>
> Signed-off-by: Thierry Reding <treding at nvidia.com>

Applied to u-boot/master, thanks!

-- 
Tom
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