netdev - RE: [next-queue PATCH] igb: Fix the transmission mode of queue 0 for Qav mode

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Date:   Sat, 14 Apr 2018 02:28:13 +0000
From:   "Brown, Aaron F" <aaron.f.brown@...el.com>
To:     "Gomes, Vinicius" <vinicius.gomes@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC:     "Gomes, Vinicius" <vinicius.gomes@...el.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Sanchez-Palencia, Jesus" <jesus.sanchez-palencia@...el.com>,
        "Guedes, Andre" <andre.guedes@...el.com>
Subject: RE: [next-queue PATCH] igb: Fix the transmission mode of queue 0
 for Qav mode

> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of Vinicius Costa Gomes
> Sent: Friday, March 30, 2018 5:07 PM
> To: intel-wired-lan@...ts.osuosl.org
> Cc: Gomes, Vinicius <vinicius.gomes@...el.com>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher@...el.com>; netdev@...r.kernel.org; Sanchez-Palencia,
> Jesus <jesus.sanchez-palencia@...el.com>; Guedes, Andre
> <andre.guedes@...el.com>
> Subject: [next-queue PATCH] igb: Fix the transmission mode of queue 0 for
> Qav mode
> 
> When Qav mode is enabled, queue 0 should be kept on Stream Reservation
> mode. From the i210 datasheet, section 8.12.19:
> 
> "Note: Queue0 QueueMode must be set to 1b when TransmitMode is set to
> Qav." ("QueueMode 1b" represents the Stream Reservation mode)
> 
> The solution is to give queue 0 the all the credits it might need, so
> it has priority over queue 1.
> 
> A situation where this can happen is when cbs is "installed" only on
> queue 1, leaving queue 0 alone. For example:
> 
> $ tc qdisc replace dev enp2s0 handle 100: parent root mqprio num_tc 3 \
>      	   map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 queues 1@0 1@1 2@2 hw 0
> 
> $ tc qdisc replace dev enp2s0 parent 100:2 cbs locredit -1470 \
>      	   hicredit 30 sendslope -980000 idleslope 20000 offload 1
> 
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 

Tested by: Aaron Brown <aaron.f.brown@...el.com>