From: Ido Schimmel <ido...@mellanox.com>
Date: Wed, 31 Oct 2018 09:56:41 +0000
> Petr says:
>
> An MC-aware mode was introduced in commit 7b8195306694 ("mlxsw:
> spectrum: Configure MC-aware mode on mlxsw ports"). In MC-aware mode,
> BUM traffic gets a special treatment by being assigned to a separate set
> of traffic classes 8..15. Pairs of TCs 0 and 8, 1 and 9, etc., are then
> configured to strictly prioritize the lower-numbered ones. The intention
> is to prevent BUM traffic from flooding the switch and push out all UC
> traffic, which would otherwise happen, and instead give UC traffic
> precedence.
>
> However strictly prioritizing UC traffic has the effect that UC overload
> pushes out all BUM traffic, such as legitimate ARP queries. These
> packets are kept in queues for a while, but under sustained UC overload,
> their lifetime eventually expires and these packets are dropped. That is
> detrimental to network performance as well.
>
> In this patchset, MC TCs (8..15) are configured with minimum shaper of
> 200Mbps (a minimum permitted value) to allow a trickle of necessary
> control traffic to get through.
>
> First in patch #1, the QEEC register is extended with fields necessary
> to configure the minimum shaper.
>
> In patch #2, minimum shaper is enabled on TCs 8..15.
>
> In patches #3 and #4, first the MC-awareness test is tweaked to support
> the minimum shaper, and then a new test is introduced to test that MC
> traffic behaves well under UC overload.
Series applied, thanks.
