Re: CLOCK_MONOTONIC datagram timestamps by the kernel

From: Stephen Hemminger <shemminger@linux-foundation.org>
To: Eric Dumazet <dada1@cosmosbay.com>
Cc: John find <linux.kernel@free.fr>,
	linux-net@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: CLOCK_MONOTONIC datagram timestamps by the kernel
Date: Thu, 01 Mar 2007 07:54:44 -0800	[thread overview]
Message-ID: <45E6F744.8070106@linux-foundation.org> (raw)
In-Reply-To: <200703011230.50596.dada1@cosmosbay.com>

Eric Dumazet wrote:
> On Wednesday 28 February 2007 17:07, John wrote:
>
>   
>> Consider an idle Linux 2.6.20-rt8 system, equipped with a single PCI-E
>> gigabit Ethernet NIC, running on a modern CPU (e.g. Core 2 Duo E6700).
>> All this system does is time stamp 1000 packets per second.
>>
>> Are you claiming that this platform *cannot* handle most packets within
>> less than 1 microsecond of their arrival?
>>     
>
> Yes I claim it.
>
> You expect too much of this platform, unless "most" means 10 % for 
> you ;)
>
> If you replace "1 us" by "50 us", then yes, it probably can do it, if "most" 
> means 99%, (not 99.999 %)
>
> Anyway, if you want to play, you can apply this patch on top of 
> linux-2.6.21-rc2  (nanosecond resolution infrastruture needs 2.6.21)
> I let you do the adjustments for rt kernel.
>
>   
I like it except changing stamp to stampns all over the place is 
unnecessary, just change the
type.

> I compiled it on my i386 machine, and tested it with a patched libpcap/tcpdump
>
>   
I assume old tcpdump works as expected.