[Intel-wired-lan] [next-queue PATCH] igb: Fix the transmission mode of queue 0 for Qav mode

[Brown, Aaron F]

> From: netdev-owner at vger.kernel.org [mailto:netdev-
> owner at vger.kernel.org] On Behalf Of Vinicius Costa Gomes
> Sent: Friday, March 30, 2018 5:07 PM
> To: intel-wired-lan at lists.osuosl.org
> Cc: Gomes, Vinicius <vinicius.gomes at intel.com>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher at intel.com>; netdev at vger.kernel.org; Sanchez-Palencia,
> Jesus <jesus.sanchez-palencia at intel.com>; Guedes, Andre
> <andre.guedes at intel.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 at 0 1 at 1 2 at 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 at intel.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 

Tested by: Aaron Brown <aaron.f.brown at intel.com>