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Subject: Re: How much we can trust packet timestamping
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: uaca@alumni.uv.es
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <20021230112838.GA928@pusa.informat.uv.es>
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Date: 30 Dec 2002 13:09:03 +0000
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On Mon, 2002-12-30 at 11:28, uaca@alumni.uv.es wrote:
> Hi all
> 
> IMHO The problem is quite complicated because
> 
> + common hardware is not designed for real time:
> 
> 	- sends multiple PDUs within one interrupt, and can be delayed
> 	- Host adapter bus & infraestructure is not designed to garantee latency
>   	etc...

The packet can be timestamped by the hardware receiving as well as by
the kernel netif_rx code. This is actually intentional and there is
hardware that supports doing IRQ raise time sampling which the driver
can then use to get very accurate data.

Alan

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