netdev - Re: [RFC PATCH net-next 4/6] ptp: Support time stamps based on free running time

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Message-ID: <20220306164220.GB6290@hoboy.vegasvil.org>
Date:   Sun, 6 Mar 2022 08:42:20 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     yangbo.lu@....com, davem@...emloft.net, kuba@...nel.org,
        mlichvar@...hat.com, vinicius.gomes@...el.com,
        netdev@...r.kernel.org
Subject: Re: [RFC PATCH net-next 4/6] ptp: Support time stamps based on free
 running time

On Sun, Mar 06, 2022 at 09:56:56AM +0100, Gerhard Engleder wrote:

> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 2be263184d1e..2ec8d944a557 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -521,6 +521,8 @@ static inline bool skb_frag_must_loop(struct page *p)
>   * struct skb_shared_hwtstamps - hardware time stamps
>   * @hwtstamp:	hardware time stamp transformed into duration
>   *		since arbitrary point in time
> + * @hwfreeruntstamp:	hardware time stamp based on free running time
> + *			transformed into duration since arbitrary point in time
>   *
>   * Software time stamps generated by ktime_get_real() are stored in
>   * skb->tstamp.
> @@ -533,6 +535,7 @@ static inline bool skb_frag_must_loop(struct page *p)
>   */
>  struct skb_shared_hwtstamps {
>  	ktime_t	hwtstamp;
> +	ktime_t	hwfreeruntstamp;

You are adding eight bytes per frame for what is arguably an extreme
niche case.  I personally wouldn't mind, but expect push back from the
rest of the world!

Maybe this should hide behind a Kconfig option with default off.

@davem, @kuba, what do you think?

>  };
>  
>  /* Definitions for tx_flags in struct skb_shared_info */
> -- 
> 2.20.1
> 

Thanks,
Richard