Re: CLOCK_MONOTONIC datagram timestamps by the kernel

From: Stephen Hemminger
Date: Thu Mar 01 2007 - 10:55:52 EST


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.
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