option FIB_ALGO and dpdk_lpm4

[Alexander V. Chernikov]

24.02.2021, 10:50, "Olivier Cochard-Labbé" <olivier at freebsd.org>:
> On Wed, Feb 24, 2021 at 1:22 AM Marek Zarychta <
> zarychtam at plan-b.pwste.edu.pl> wrote:
>
>>  >
>>
>>  Please let me ask only one final question. Does adding:
>>
>>  net.route.algo.inet.algo=dpdk_lpm4
>>  net.route.algo.inet6.algo=dpdk_lpm6
>>
>>  to /etc/sysctl.conf make any sense? I see that right FIB_ALGO is
>>  automatically picked up when the module is available.
>
> My understanding is the network stack will switch to the optimum algorithm
> regarding the number of routes installed.
> cf "Automatic algorithm selection" chapter here:
> https://reviews.freebsd.org/D27401
>
> So you don't need to set this sysctl.
To add some points to Olivier's explanation:
indeed, algorithm selection SHOULD happen automatically.
Some things to keep in mind: when the BGP sessions flaps kernel routes may go from the full-view to near-zero and vice versa.
In that case, automatic selection will switch to lockless_radix for the range between 10..1000 routes (or similar). Lockless radix schedules rebuild for every change, so the speed of deleting/adding first 1k routes may be slower than expected.

>
> Regards,
>
> Olivier
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