netdev - Re: [PATCH] NET : convert network timestamps to ktime

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Date:	Fri, 02 Mar 2007 23:46:14 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
CC:	David Miller <davem@...emloft.net>,
	John find <linux.kernel@...e.fr>, netdev@...r.kernel.org
Subject: Re: [PATCH] NET : convert network timestamps to ktime_t

Stephen Hemminger a écrit :
> On Fri, 2 Mar 2007 15:38:41 +0100
> Eric Dumazet <dada1@...mosbay.com> wrote:
> 
>> We currently use a special structure (struct skb_timeval) and plain 'struct 
>> timeval' to store packet timestamps in sk_buffs and struct sock.
>>
>> This has some drawbacks :
>> - Fixed resolution of micro second.
>> - Waste of space on 64bit platforms where sizeof(struct timeval)=16
>>
>> I suggest using ktime_t that is a nice abstraction of high resolution time 
>> services, currently capable of nanosecond resolution.
>>
>> As sizeof(ktime_t) is 8 bytes, using ktime_t in 'struct sock' permits a 8 byte 
>> shrink of this structure on 64bit architectures. Some other structures also 
>> benefit from this size reduction (struct ipq in ipv4/ip_fragment.c, struct 
>> frag_queue in ipv6/reassembly.c, ...)
>>
>>
> 
> You missed a couple of spots.

Arg yes...

> 
> --- tcp-2.6.orig/net/sunrpc/svcsock.c	2007-03-02 12:50:45.000000000 -0800
> +++ tcp-2.6/net/sunrpc/svcsock.c	2007-03-02 12:58:28.000000000 -0800
> @@ -805,16 +805,9 @@
>  		/* possibly an icmp error */
>  		dprintk("svc: recvfrom returned error %d\n", -err);
>  	}
> -	if (skb->tstamp.off_sec == 0) {
> -		struct timeval tv;
>  
> -		tv.tv_sec = xtime.tv_sec;
> -		tv.tv_usec = xtime.tv_nsec / NSEC_PER_USEC;
> -		skb_set_timestamp(skb, &tv);
> -		/* Don't enable netstamp, sunrpc doesn't
> -		   need that much accuracy */
> -	}
> -	skb_get_timestamp(skb, &svsk->sk_sk->sk_stamp);
> +	svsk->sk_sk->sk_stamp = (skb->tstamp.tv64 != 0) ? skb->tstamp
> +		: ktime_get_real();

Well, if we want to stay in the spirit of old code, we probably want to use 
current_kernel_time() (+ timespec_to_ktime()), because its less expensive.

And also setting the skb tstamp, no ?


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