From: Andy Furniss <andy.furniss@dsl.pipex.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] SFQ latency
Date: Wed, 19 May 2004 10:58:17 +0000 [thread overview]
Message-ID: <40AB3DC9.9010403@dsl.pipex.com> (raw)
In-Reply-To: <200405191221.30730.haden@homelan.lt>
Tomas Simonaitis wrote:
> Anyone notices that using sfq qdisc adds latency compared to pfifo?
>
> With "sfq perturb 10" ping latency is around 100-120ms, while with "pfifo
> limit 3" drops to ~10-30ms (qdiscs belong to htb class).
>
> I'm missing something or is this expected?
>
> {
> $TC_CLASS parent 1:1 classid 1:20 htb prio 0 rate 900kbit ceil 1000kbit burst
> 7k
> $TC_QDISC parent 1:20 handle 200: {pfifo limit 3} | {sfq perturb 10}
> }
There shouldn't really be a queue as such (you still choose one) for
your interactive traffic - if you really care about latency HTB should
have a class with a high (low number) prio and a high rate (> expected
traffic), so other traffic has to borrow.
If you do end up queueing your interractive, then pfifo limit 3 means
there will only be 2 packets in front of the ping (I suppose bfifo would
be nicer as a fall back - it will penalise big packets more, WRT drops).
SFQ default qlen is 128, though the way it works means the delay will
depend on how many other connections are queued.
Andy.
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next prev parent reply other threads:[~2004-05-19 10:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-05-19 9:21 [LARTC] SFQ latency Tomas Simonaitis
2004-05-19 10:58 ` Andy Furniss [this message]
2004-05-19 13:23 ` Tomas Simonaitis
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