[Buildroot] [PATCH 1/1] package/busybox: speed up DHCP lease acquisition

[Angelo Compagnucci]

Il giorno sab 13 ago 2022 alle ore 22:53 Edgar Bonet
<bonet at grenoble.cnrs.fr> ha scritto:
>
> Commit c343e01ac4908f76520cf9a405ed87650e78dc62 made udhcpc send a
> single DHCP request (instead of 3) before going to the background, thus
> speeding up the boot process if the DHCP lease is not obtained
> immediately. Unfortunately, this can also slow down the acquisition of
> the lease as, after going to the background, udhcpc waits for 20 seconds
> (instead of 3) before retrying.
>
> Speed up the lease acquisition by setting the retry timeout to 3
> seconds.
>
> Signed-off-by: Edgar Bonet <bonet at grenoble.cnrs.fr>
> ---
> Hello!
>
> While testing 2022.08-rc1 with acmesystems_acqua_a5_512mb_defconfig on a
> real Acqua board (and Ubuntu 20.04 host), I noticed that my board became
> very slow in getting a DHCP lease, which was a fast process on 2022.05.
> Wireshark showed the following DHCP traffic ("<" = received from the
> board, ">" = sent to the board):
>
>     time (s)  packet
>     ---------------------
>     03.24 < DHCP Discover
>     06.24 > DHCP Offer
>     26.28 < DHCP Discover
>     26.28 > DHCP Offer
>     26.28 < DHCP Request
>     26.28 > DHCP ACK
>
> Looking at the log 2022.05..2022.08-rc1, I identified the regression to
> be in commit c343e01ac4908f76520cf9a405ed87650e78dc62. This commit adds
> the option -t1 to the udhcpc command, which makes it go to the
> background after only one try, and has the unfortunate side effect of
> introducing a 20-second delay.
>
> With this patch applied, the lease is acquired much faster:
>
>     03.26 < DHCP Discover
>     06.26 > DHCP Offer
>     09.28 < DHCP Discover
>     09.29 > DHCP Offer
>     09.29 < DHCP Request
>     09.29 > DHCP ACK
>
> Regards,

While I'm ok with this patch, I suggest checking why obtaining the
lease fails on your board on the first try.

The intent of adding -t1 was to speed up the boot process not wasting
time waiting foreground: this can be generically applied to any board:
the network cable could be unplugged and this shouldn't affect the
boot process time.

The patch you propose here instead tries to solve a problem you have
with your board: the board doesn't obtain the lease timely (first try)
and then you want a faster retry.
I think this is not generic enough to be acceptable for all the
boards, you can solve this problem easily on your local busybox
defconfig.

Anyway I'm not against changing the default background retry timeout
if this is not harming other users.

>
> Edgar.
>
>  package/busybox/busybox.config | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/package/busybox/busybox.config b/package/busybox/busybox.config
> index 2409cbcce1..137e44c870 100644
> --- a/package/busybox/busybox.config
> +++ b/package/busybox/busybox.config
> @@ -1022,7 +1022,7 @@ CONFIG_UDHCP_DEBUG=0
>  CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS=80
>  CONFIG_FEATURE_UDHCP_RFC3397=y
>  CONFIG_FEATURE_UDHCP_8021Q=y
> -CONFIG_IFUPDOWN_UDHCPC_CMD_OPTIONS="-t1 -b -R -O search"
> +CONFIG_IFUPDOWN_UDHCPC_CMD_OPTIONS="-t1 -A3 -b -R -O search"
>
>  #
>  # Print Utilities
> --
> 2.25.1
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