netdev - Re: [net 2/6] igb: Fix the transmission mode of queue 0 for Qav mode

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Date:   Wed, 25 Apr 2018 12:27:30 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net
Cc:     Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
        jogreene@...hat.com
Subject: Re: [net 2/6] igb: Fix the transmission mode of queue 0 for Qav mode

On 4/24/2018 10:29 PM, Jeff Kirsher wrote:

> From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> 
> When Qav mode is enabled, queue 0 should be kept on Stream Reservation

    s/on/in/?

> 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>
> Tested-by: Aaron Brown <aaron.f.brown@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
[...]

MBR, Sergei