From: Kabelweb <office@kabelweb.at>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] Problems using The Ultimate Traffic Conditioner from the Cookbook
Date: Thu, 25 Dec 2003 08:43:17 +0000 [thread overview]
Message-ID: <marc-lartc-107234235125631@msgid-missing> (raw)
In-Reply-To: <marc-lartc-107181174021910@msgid-missing>
Hi!
> So I played a bit with the DOWNLINK value and found out that down to and
> including 555 no packets are dropped even if a download fully saturates the
> link while 554 already drastically caps the download to ~65 kbytes/s, and
> there are packets being dropped:
It seems that your setup suffers from timer inaccuracy.
This topic has been dealt with some times on this list.
Read (for example) this thread:
http://www.mail-archive.com/lartc@mailman.ds9a.nl/msg02795.html
In short: it might be that the timer of your qdisc runs at to low a resolution
to measure exactly how much packets to let pass since the last time it could
send. Therefore it seems that the bandwith cap of the qdisc does not
correlate linear with the given kbps value but more or less like a staircase
(ie. a dramatic drop on a certain kbps value - like you described it at
554kbps)
> Lower values than 554 drop even more packets, just as I'd expect; there
> seems to be no other threshold as hard as from 554 to 555.
The stairs should get smaller with the kbps value specified but should remain
stairs and not become a linear slope - assuming I've guessed the source of
your problem correctly.
The solution (as mentioned in the thread above) is to either change the HZ
value to for example 1024 (you don't have to do this by manually patching
your kernel source because your gentoo kernel has a patch applied which lets
you specify the HZ value from kernel config - I think its somewhere in
"Processor type and features") or to change PSCHED_CLOCK_SOURCE to PSCHED_CPU
in your /usr/src/linux/include/net/pkt_sched.h (which I personally had some
problems with in the past - can't remember exactly though).
I hope this helps - let us know...
Andreas
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next prev parent reply other threads:[~2003-12-25 8:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-12-19 5:06 [LARTC] Problems using The Ultimate Traffic Conditioner from the Cookbook Malte Starostik
2003-12-25 8:43 ` Kabelweb [this message]
2003-12-28 8:31 ` Malte Starostik
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