Messages in this thread | | | Date | Mon, 28 Feb 2011 09:20:28 -0800 | Subject | Re: txqueuelen has wrong units; should be time | From | Bill Sommerfeld <> |
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On Mon, Feb 28, 2011 at 07:38, Hagen Paul Pfeifer <hagen@jauu.net> wrote: > On Sun, 27 Feb 2011 18:33:39 -0500, Albert Cahalan wrote: >> I suppose there is a need to allow at least 2 packets despite any >> time limits, so that it remains possible to use a traditional modem >> even if a huge packet takes several seconds to send. > > That is a good point! We talk about as we may know every use case of > Linux. But this is not true at all. One of my customer for example operates > the Linux network stack functionality on top of a proprietary MAC/Driver > where the current packet queue characteristic is just fine. The > time-drop-approach is unsuitable because the bandwidth can vary in a small > amount of time over a great range (0 till max. bandwidth). A sufficient > buffering shows up superior in this environment (only IPv{4,6}/UDP).
The tension is between the average queue length and the maximum amount of buffering needed. Fixed-sized tail-drop queues -- either long, or short -- are not ideal.
My understanding is that the best practice here is that you need (bandwidth * path delay) buffering to be available to absorb bursts and avoid drops, but you also need to use queue management algorithms with ECN or random drop to keep the *average* queue length short; unfortunately, researchers are still arguing about the details of the second part...
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