Subject: Re: [RFC v3 net-next 08/18] net: SO_TXTIME: Add clockid and drop_if_late params

From: Eric Dumazet <[email-masked]>
Date: Tue, 06 Mar 2018 18:53:29 -0800

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 ?