netdev - Re: [PATCH net 0/4] mlxsw: Enable minimum shaper on MC TCs

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Date:   Wed, 31 Oct 2018 12:57:14 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     idosch@...lanox.com
Cc:     netdev@...r.kernel.org, jiri@...lanox.com, petrm@...lanox.com,
        mlxsw@...lanox.com
Subject: Re: [PATCH net 0/4] mlxsw: Enable minimum shaper on MC TCs

From: Ido Schimmel <idosch@...lanox.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.