netdev - Re: [net-next] net: change accept_ra_min_rtr

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Date: Wed, 26 Jul 2023 14:03:36 -0600
From: David Ahern <dsahern@...nel.org>
To: Patrick Rohr <prohr@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
 Linux Network Development Mailing List <netdev@...r.kernel.org>,
 Maciej Żenczykowski <maze@...gle.com>,
 Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [net-next] net: change accept_ra_min_rtr_lft to affect all RA
 lifetimes

On 7/26/23 11:33 AM, Patrick Rohr wrote:
>> The commit mentioned in the Fixes was just applied and you are already
>> sending a follow up moving the same code around again.
> 
> I got feedback off of the mailing list after the patch was applied.

That offlist discussion should be summarized in the commit message (text
below?)

> In order for
> the sysctl to be useful to Android, it should really apply to all lifetimes in
> the RA, since that is what determines the minimum frequency at which RAs must be
> processed by the kernel. Android uses hardware offloads to drop RAs
> for a fraction of the
> minimum of all lifetimes present in the RA (some networks have very
> frequent RAs (5s) with high lifetimes (2h)). Despite this, we have
> encountered
> networks that set the router lifetime to 30s which results in very frequent CPU
> wakeups. Instead of disabling IPv6 (and dropping IPv6 ethertype in the
> WiFi firmware)
> entirely on such networks, it seems better to ignore such routers
> while still processing RAs from other IPv6 routers on the same network
> (i.e. to support IoT applications).
> The previous implementation dropped the entire RA
> based on router lifetime. This turned out to be hard to expand to the other
> lifetimes present in the RA in a consistent manner -- dropping the
> entire RA based on
> RIO/PIO lifetimes would essentially require parsing the whole thing twice. I am
> sending this follow up patch now to fix 1671bcfd76fd before it is released.
>