netdev - Re: [PATCH] pkt_sched: fq: rate limiting improvements

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Date:	Tue, 01 Oct 2013 13:01:14 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, sesse@...gle.com
Subject: Re: [PATCH] pkt_sched: fq: rate limiting improvements

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 01 Oct 2013 09:10:16 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> FQ rate limiting suffers from two problems, reported
> by Steinar :
> 
> 1) FQ enforces a delay when flow quantum is exhausted in order
> to reduce cpu overhead. But if packets are small, current
> delay computation is slightly wrong, and observed rates can
> be too high.
> 
> Steinar had this problem because he disabled TSO and GSO,
> and default FQ quantum is 2*1514.
> 
> (Of course, I wish recent TSO auto sizing changes will help
> to not having to disable TSO in the first place)
> 
> 2) maxrate was not used for forwarded flows (skbs not attached
> to a socket)
> 
> Tested:
> 
> tc qdisc add dev eth0 root est 1sec 4sec fq maxrate 8Mbit
> netperf -H lpq84 -l 1000 &
> sleep 10 ; tc -s qdisc show dev eth0
> qdisc fq 8003: root refcnt 32 limit 10000p flow_limit 100p buckets 1024
>  quantum 3028 initial_quantum 15140 maxrate 8000Kbit 
>  Sent 16819357 bytes 11258 pkt (dropped 0, overlimits 0 requeues 0) 
>  rate 7831Kbit 653pps backlog 7570b 5p requeues 0 
>   44 flows (43 inactive, 1 throttled), next packet delay 2977352 ns
>   0 gc, 0 highprio, 5545 throttled
> 
> lpq83:~# tcpdump -p -i eth0 host lpq84 -c 12
> 09:02:52.079484 IP lpq83 > lpq84: . 1389536928:1389538376(1448) ack 3808678021 win 457 <nop,nop,timestamp 961812 572609068>
> 09:02:52.079499 IP lpq83 > lpq84: . 1448:2896(1448) ack 1 win 457 <nop,nop,timestamp 961812 572609068>
> 09:02:52.079906 IP lpq84 > lpq83: . ack 2896 win 16384 <nop,nop,timestamp 572609080 961812>
> 09:02:52.082568 IP lpq83 > lpq84: . 2896:4344(1448) ack 1 win 457 <nop,nop,timestamp 961815 572609071>
> 09:02:52.082581 IP lpq83 > lpq84: . 4344:5792(1448) ack 1 win 457 <nop,nop,timestamp 961815 572609071>
> 09:02:52.083017 IP lpq84 > lpq83: . ack 5792 win 16384 <nop,nop,timestamp 572609083 961815>
> 09:02:52.085678 IP lpq83 > lpq84: . 5792:7240(1448) ack 1 win 457 <nop,nop,timestamp 961818 572609074>
> 09:02:52.085693 IP lpq83 > lpq84: . 7240:8688(1448) ack 1 win 457 <nop,nop,timestamp 961818 572609074>
> 09:02:52.086117 IP lpq84 > lpq83: . ack 8688 win 16384 <nop,nop,timestamp 572609086 961818>
> 09:02:52.088792 IP lpq83 > lpq84: . 8688:10136(1448) ack 1 win 457 <nop,nop,timestamp 961821 572609077>
> 09:02:52.088806 IP lpq83 > lpq84: . 10136:11584(1448) ack 1 win 457 <nop,nop,timestamp 961821 572609077>
> 09:02:52.089217 IP lpq84 > lpq83: . ack 11584 win 16384 <nop,nop,timestamp 572609090 961821>
> 
> Reported-by: Steinar H. Gunderson <sesse@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks a lot Eric.
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