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LWN.net Weekly Edition for May 16, 2013
A look at the PyPy 2.0 release
PostgreSQL 9.3 beta: Federated databases and more
LWN.net Weekly Edition for May 9, 2013
(Nearly) full tickless operation in 3.10
However, it would be nice to do it automatically.
Power impact of debufferbloating
Posted Sep 14, 2011 6:26 UTC (Wed) by njs (guest, #40338)
Actually, there is one other way to make traffic shaping work -- if you throttle your outgoing bandwidth, then that throttling is applied in between the qdisc and the device buffers, so the device buffers stop filling up. Lots of docs on traffic shaping say that this is a good idea to work around problems with your ISP's queue management, but in fact it's needed just to work around problems within your own kernel's queue management. Also, you can't really do it for wifi since you don't know what the outgoing bandwidth is at any given time, and in the case of 802.11n, this will actually *reduce* that bandwidth because hiding packets from the device driver will screw up its ability to do aggregation.
Posted Sep 14, 2011 14:34 UTC (Wed) by Cyberax (✭ supporter ✭, #52523)
In my own tests, I was able to segregate heavy BitTorrent traffic from VoIP traffic and get good results on a puny 2MBit line.
I did lost some bandwidth, but not that much.
Posted Sep 14, 2011 16:37 UTC (Wed) by njs (guest, #40338)
There isn't much the qdisc can do here, prioritization-wise -- even if packet 2 turns out to be high priority, it can't "take back" packet 1 and send packet 2 first. Packet 1 is already gone.
In your tests you used bandwidth throttling, which moved the chokepoint so that it fell in between the qdisc buffer and your device buffer. You told the qdisc to hold onto packets and only let them dribble out at a fixed rate, and chose that rate so that it would be slower than the rate the device buffer drained. So the device buffer never filled up, and the qdisc actually had multiple packets visible at once and was able to reorder them.
Posted Sep 29, 2011 0:02 UTC (Thu) by marcH (subscriber, #57642)
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