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Date: Sat, 30 Mar 2013 08:28:51 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Markus Trippelsdorf <markus@...ppelsdorf.de> Cc: Vijay Subramanian <subramanian.vijay@...il.com>, netdev@...r.kernel.org, davem@...emloft.net Subject: Re: [PATCH net] net: fq_codel: Fix off-by-one error On Sat, 2013-03-30 at 16:08 +0100, Markus Trippelsdorf wrote: > This is exactly the setup that I'm using right now (prio + 4 fq_codel > with bittorent set to low). > And setting the fq_codel limit to 1024 improves latency in this > situation. > That's all I wanted to communicate. If the result doesn't interest you, > just ignore my mail. > I didn't ignore your mail, I spent time from my Saturday to answer you. If your prio setting was right, a limit of 10 should be enough for the high prio queue, and a mere pfifo would be ok. By definition, high prio packets should have a minimum latency (assuming of course that BQL is enabled on your device) Then, if all your packets land into he same prio queue, classification is not correct. If your link is oversubscribed (and Bittorent tends to push links to over subscribed situation), then you want to increase drops by reducing queue lengths. fq_codel default limit is only a hint, like all defaults. Some users want to increase it, others want to decrease it. In your case, I suspect the number of flows is too large (and you get hash collisions in fq), _and_ your ping packets land the crowded fq_codel qdisc, instead of a small queue reserved for high prio packets. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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