[LARTC] Re: measuring queueing delay using iproute2

[LARTC] Re: measuring queueing delay using iproute2

[Don Cohen]

How about this:
 use tcpdump to record the packets of that class
 match up the incoming and outgoing packets
 take the difference in tcp timestamps

 > From: Radhakrishnan Vijay <vijayr13@yahoo.com>
 > To: lartc@mailman.ds9a.nl
 > Subject: [LARTC] measuring queueing delay using iproute2
 > 
 > I am using the tc functionality provided by iproute2
 > to setup classes and queueing disciplines. I have a
 > requirement to determine the queueing delay of each
 > packet belonging to a particular class so that i can
 > measure the average queueing delay over a time
 > interval for a particular traffic class. I would be
 > grateful if somebody could give me pointers on how i
 > possibly can achieve this. I suspect that i would have
 > to modify the source code of iproute2 , but am not too
 > sure on what segment of the code i should be
 > modifying.
It won't help to modify iproute2.  It's not doing the forwarding. 
It only tells the kernel what you want the kernel to do.
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Re: [LARTC] Re: measuring queueing delay using iproute2

[bert hubert]

On Wed, Feb 27, 2002 at 08:57:11AM -0800, Don Cohen wrote:
> 
> How about this:
>  use tcpdump to record the packets of that class
>  match up the incoming and outgoing packets
>  take the difference in tcp timestamps

Won't work - tcpdump sits before the packet scheduler, and not after.

Regards,

bert

-- 
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Re: [LARTC] Re: measuring queueing delay using iproute2

[Don Cohen]

bert hubert writes:
 > On Wed, Feb 27, 2002 at 08:57:11AM -0800, Don Cohen wrote:
 > > 
 > > How about this:
 > >  use tcpdump to record the packets of that class
 > >  match up the incoming and outgoing packets
 > >  take the difference in tcp timestamps
 > 
 > Won't work - tcpdump sits before the packet scheduler, and not after.

No way.  For instance, the packet scheduler can decide to drop the
packet.  In which case it better not show up in tcpdump!
Tcpdump is after dequeue, just before giving the packet to the device.
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