[Cake] Long-RTT broken again
moeller0 at gmx.de
Tue Nov 3 12:46:35 EST 2015
On Nov 3, 2015, at 18:33 , Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> Jonathan Morton <chromatix99 at gmail.com> writes:
>>> Which is the same data that Cake uses. Hmm, weird…
>> No, Cake uses skb->truesize for this particular purpose. It uses
>> qdisc_pkt_len(skb) only for timing purposes.
> Ah, right. Well, I would consider that a bug. If we're doing a "max
> queue size" it should (conceptually) be in packet data units. A hard
> memory limit may make sense *in addition*, but then that should be a
> separate safeguard IMO.
I guess I have constantly been talking about a different limit than you, sorry. I was and still am advocating for the hard memory limit. But I maintain that as the kernel typically uses 2KB skis per packet (independent of packet size, as long as MTU = 1500 or so) the packet limit will also do double duty as memory limit. Then again the max queue size in packets is more an implementation thing in my mind ;) I believe the only people changing limit will not be people thinking about how many packets they want queued maximally, but rather those that want to avoid OOM; from that view a memory limit seems quite natural. So maybe we need a min(max_packets, consumed_queue_memory) as true limit? Potentially with a notification if there is a large effective difference between the two?
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