On 08/01/11 12:41, Camaleón wrote:
On Sat, 08 Jan 2011 11:16:39 +0000, Alan Chandler wrote:After a Slashdot entry, I discovered an interesting series of blog posts by Jim Gettys. The series starts http://gettys.wordpress.com/2010/10/02/first-puzzle-piece/ (unlike Slashdot which linked to a random place in the middle).... How to set txqueuelen? http://www.debian-administration.org/users/ajt/weblog/188 Question is why should we manually tweak that value at all? Are the defaults bad/incorrectly set or are they very conservative? What is the gain to increasing it? Will it have any drawbacks? What happens with "bonded" interfaces (mode 1 or mode 3)? :-?
If you read Jim's blog articles, he basically argues that the built in TCP congestion control mechanisms are blunted because there is a delay in noticing congestion build up as the buffers fill up. The effect is that on congested links, latency and jitter can become very high (several seconds).
With memory so cheap these days, the tendancy has been to increase available buffering to the point where there is far too much of it. This means that the problem of jitter and latency has got worse
He is suggesting that since most ethernet chips have internal ring buffers that txqueuelen should be set to 0.
I must admit I notice sometimes at home when playing youtube videos - it has all been running smoothly for a while and then suddenly you get into buffering mode over and over again.
I thought I might experiment with setting txqueuelen to 0 to see what difference it made.
-- Alan Chandler http://www.chandlerfamily.org.uk