netdev - Re: [RFC v3 net-next 08/18] net: SO_TXTIME: Add clockid and drop_if

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Date:   Tue, 06 Mar 2018 18:53:29 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>,
        netdev@...r.kernel.org
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        vinicius.gomes@...el.com, richardcochran@...il.com,
        intel-wired-lan@...ts.osuosl.org, anna-maria@...utronix.de,
        henrik@...tad.us, tglx@...utronix.de, john.stultz@...aro.org,
        levi.pearson@...man.com, edumazet@...gle.com, willemb@...gle.com,
        mlichvar@...hat.com
Subject: Re: [RFC v3 net-next 08/18] net: SO_TXTIME: Add clockid and
 drop_if_late params

On Tue, 2018-03-06 at 17:12 -0800, Jesus Sanchez-Palencia wrote:
> Extend SO_TXTIME APIs with new per-packet parameters: a clockid_t and
> a drop_if_late flag. With this commit the API becomes:
> 
> 

 * diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
 * index d8340e6e8814..951969ceaf65 100644
 * --- a/include/linux/skbuff.h
 * +++ b/include/linux/skbuff.h
 * @@ -788,6 +788,9 @@ struct sk_buff {
 *  	__u8			tc_redirected:1;
 *  	__u8			tc_from_ingress:1;
 *  #endif
 * +	__u8			tc_drop_if_late:1;
 * +
 * +	clockid_t		txtime_clockid;
 *  
 *  #ifdef CONFIG_NET_SCHED
 *  	__u16			tc_index;	/* traffic
   control index */


This is adding 32+1 bits to sk_buff, and possibly holes in this very
very hot (and already too fat) structure.

Do we really need 32 bits for a clockid_t ?