Re: Buffer Bloat, and what to do about it in Debian
On Sun, 09 Jan 2011 08:57:45 +0000, Alan Chandler wrote:
> 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.
True is that I saw no explicit reference to completey disable
"txqueuelen" value on the above article but maybe I misread it :-?
> 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.
Oh, me too. But do you think this can be related to the value of this
parameter? I tend to blame my ISP or the remote server for being so
slow :-)
> I thought I might experiment with setting txqueuelen to 0 to see what
> difference it made.
I'm still not sure about that change and its benefits in the whole system
no just for multimedia streaming purposes.
Greetings,
--
Camaleón
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