netdev - Re: [PATCH 1/1] can: dev: add software tx timestamps

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Date:   Sun, 10 Jan 2021 12:29:13 +0100
From:   Jeroen Hofstee <jhofstee@...tronenergy.com>
To:     Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-can@...r.kernel.org
Cc:     Wolfgang Grandegger <wg@...ndegger.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] can: dev: add software tx timestamps

Hello Vincent,

On 1/10/21 11:35 AM, Vincent Mailhol wrote:
> Call skb_tx_timestamp() within can_put_echo_skb() so that a software
> tx timestamp gets attached on the skb.
>
[..]
>
> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
> index 3486704c8a95..3904e0874543 100644
> --- a/drivers/net/can/dev.c
> +++ b/drivers/net/can/dev.c
> @@ -484,6 +484,8 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
>   
>   		/* save this skb for tx interrupt echo handling */
>   		priv->echo_skb[idx] = skb;
> +
> +		skb_tx_timestamp(skb);
>   	} else {
>   		/* locking problem with netif_stop_queue() ?? */
>   		netdev_err(dev, "%s: BUG! echo_skb %d is occupied!\n", __func__, idx);

Personally, I would put the skb_tx_timestamp, before adding it to the array:

         /* make settings for echo to reduce code in irq context */
         skb->pkt_type = PACKET_BROADCAST;
         skb->ip_summed = CHECKSUM_UNNECESSARY;
         skb->dev = dev;
+       skb_tx_timestamp(skb);

         /* save this skb for tx interrupt echo handling */
         priv->echo_skb[idx] = skb;


I don't think it actually matters though.

Regards,

Jeroen