netdev - RE: [PATCH 2/3] mlx4: Don't bother using skb_tx_hash in mlx4_en_select

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Date:   Wed, 2 May 2018 18:09:37 +0000
From:   "Ruhl, Michael J" <michael.j.ruhl@...el.com>
To:     "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "Dalessandro, Dennis" <dennis.dalessandro@...el.com>,
        "Vishwanathapura, Niranjana" <niranjana.vishwanathapura@...el.com>,
        "tariqt@...lanox.com" <tariqt@...lanox.com>
Subject: RE: [PATCH 2/3] mlx4: Don't bother using skb_tx_hash in
 mlx4_en_select_queue

>-----Original Message-----
>From: linux-rdma-owner@...r.kernel.org [mailto:linux-rdma-
>owner@...r.kernel.org] On Behalf Of Alexander Duyck
>Sent: Friday, April 27, 2018 2:07 PM
>To: netdev@...r.kernel.org; davem@...emloft.net
>Cc: linux-rdma@...r.kernel.org; Dalessandro, Dennis
><dennis.dalessandro@...el.com>; Vishwanathapura, Niranjana
><niranjana.vishwanathapura@...el.com>; tariqt@...lanox.com
>Subject: [PATCH 2/3] mlx4: Don't bother using skb_tx_hash in
>mlx4_en_select_queue
>
>The code in the fallback path has supported XDP in conjunction with the Tx
>traffic classification for TCs for over a year now. So instead of just
>calling skb_tx_hash for every packet we are better off using the fallback
>since that will record the Tx queue to the socket and then that can be used
>instead of having to recompute the hash every time.
>
>Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
>---
> drivers/net/ethernet/mellanox/mlx4/en_tx.c |    2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
>b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
>index 6b68537..0227786 100644
>--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
>+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
>@@ -694,7 +694,7 @@ u16 mlx4_en_select_queue(struct net_device *dev,
>struct sk_buff *skb,
> 	u16 rings_p_up = priv->num_tx_rings_p_up;
>
> 	if (netdev_get_num_tc(dev))
>-		return skb_tx_hash(dev, skb);
>+		return fallback(dev, skb);
>
> 	return fallback(dev, skb) % rings_p_up;

Hi Alexander,

The final return fallback() call is doing a % rings_p_up.

Do you need to do that for the new fallback() call?

Maybe you can get rid of the netdev_get_num_tc() call altogether?

Thanks,

Mike

> }
>
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