On 4/12/07, David Miller <[EMAIL PROTECTED]> wrote:
From: Arnaldo Carvalho de Melo <[EMAIL PROTECTED]>
Date: Thu, 12 Apr 2007 18:14:54 -0300
> This patch replaces calls to do_gettimeofday at the receiver CCID 3
> with skb timestamps. The skb timestamps are computed earlier in the
> receive path, experimental measurements have shown that up to several
> hundred microseconds can lie between the skb receive timestamp and the
> timestamp taken when CCID 3 receives the packet. This difference has
> a negative impact on RTT estimation (reduced accuracy).
>
> Signed-off-by: Gerrit Renker <[EMAIL PROTECTED]>
> Acked-by: Ian McDonald <[EMAIL PROTECTED]>
> Signed-off-by: Arnaldo Carvalho de Melo <[EMAIL PROTECTED]>
And this creates an even deeper dependency on the global packet
timestamping facility. Those are supposed to be enabled only
in obscure circumstances because timestamping every packet is
incredibly expensive.
Please find a better way.
Well, there seems to be just one better way, to timestamp the packet
as soon as it enters the dccp stack, in dccp_v[46]_rcv, and consider
the time from the driver -> ip v[46] -> dccp_v[46]_ as "in the wire".
- Arnaldo
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