[Intel-wired-lan] using XPS on Intel i40e

[Kushal Gautam]

Hi:

Thank you for your inputs and pointing me to pktgen code.

I have tried a few things here( I have tried to borrow this logic/code from
pktgen code)

...
// I was doing
// txq = skb_get_tx_queue(skb->dev, skb);
// but it seemed that I will not be allowed to choose my desired queue
in this case.

// thus, I tried to hardcode it for the time being.
txq =  &dev->_tx[7];
local_bh_disable();

HARD_TX_LOCK(skb->dev, txq, 7);

if (unlikely(netif_xmit_frozen_or_drv_stopped(txq))) {
    ret = NETDEV_TX_BUSY;
    goto unlock;
}
// prior to this approach, I was using ndo_start_xmit directly as
// skb->dev->netdev_ops->ndo_start_xmit(skb, skb->dev);
// but, with this I was not able to use XPS, thus I was trying
netdev_start_xmit() [which ultimately invokes ndo_start_xmit]

ret = netdev_start_xmit(skb, skb->dev, txq, 0);

unlock:
HARD_TX_UNLOCK(skb->dev, txq);

local_bh_enable();

...


But, my packets are still flowing through the default Tx Queue 0. The
queue settings don't seem to have an effect here. Or, I could be mistaken
here.

I would appreciate any inputs on this.

Regards,
Kushal.

On Sun, Sep 16, 2018 at 10:04 PM Alexander Duyck <alexander.duyck at gmail.com>
wrote:

> On Sun, Sep 16, 2018 at 12:55 AM Kushal Gautam <kushal.gautam at gmail.com>
> wrote:
> >
> > Hi:
> >
> > I am using the Intel i40e driver from kernel source tree of Kernel
> 4.15.12
> > My NIC is Intel X710.
> >
> > I am composing and sending a packet from my custom kernel module as:
> >
> > ...
> > skb->dev->netdev_ops->ndo_start_xmit(skb, skb->dev);
> > ...
> >
> > Just like FDIR on the receiving side, is it possible to have a similar
> configuration on the sending side?
> >
> > For instance, I want my packets sent via kernel module to pass through
> TX-Queue 5. Right now all my packets are being sent through just Tx-Queue
> 0. And maybe after that, it would make sense to use XPS(
> https://github.com/torvalds/linux/blob/v3.13/Documentation/networking/scaling.txt#L364
> )
> >
> > Regards,
> > Kushal.
>
> Right now you are bypassing XPS entirely if you are using
> ndo_start_xmit to send you frames.
>
> You might take a look at the pktgen code in the kernel as I believe
> that has examples where they use specific queues to send packets. All
> that is really involved is updating a field in the sk_buff data
> structure before you call ndo_start_xmit.
>
> Hope that helps.
>
> - Alex
>
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