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Contact Us Post Here to Contact Site Administrators and Moderators How to Post in the The UNIX and Linux Forums NETEM - fq_codel and pfifo_fast change/add tc rule Post 303039015 by Priya Amaresh on Thursday 19th of September 2019 03:38:39 PM
Old 09-19-2019
NETEM - fq_codel and pfifo_fast change/add tc rule

HI,
I am trying to understand netem operation over Linux

when I issued tc show command i see as follows:
Code:
ing:~ tc qdisc show dev en1
qdisc mq 0: root
qdisc fq_codel 0: parent :18 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms memory_limit 32Mb ecn
qdisc fq_codel 0: parent :17 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms memory_limit 32Mb ecn
qdisc fq_codel 0: parent :16 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms memory_limit 32Mb ecn
ing:~

Now when i try to add/change tc qdisc with a loss of 0.5% I see following error:
Code:
ing:~ tc qdisc change dev en1 root netem loss 0.5%
Error: Qdisc not found. To create specify NLM_F_CREATE flag.
ing:~ tc qdisc add dev en1 root netem loss 0.5%
Error: Specified qdisc not found.
ing:~

How to fix it ??
Also i tried setting back to pfifo_fast (default netem rule) and then tried to add loss of 0.5% i see following issue
Code:
ing:~ tc qdisc add dev en1 root pfifo_fast
ing:~ tc qdisc show dev en1
qdisc pfifo_fast 8004: root refcnt 92 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
ing:~ tc qdisc add dev en1 root netem loss 0.5%
Error: Exclusivity flag on, cannot modify.
ing:~

Here again I tried deleting pfifo_fast tc rule but fq_codel got set back and where i was unable to set loss 0.5%
 

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FQ_CoDel(8)							       Linux							       FQ_CoDel(8)

NAME
CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel) SYNOPSIS
tc qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target TIME ] [ interval TIME ] [ quantum BYTES ] [ ecn | noecn ] DESCRIPTION
FQ_Codel (Fair Queuing Controlled Delay) is queuing discipline that combines Fair Queuing with the CoDel AQM scheme. FQ_Codel uses a sto- chastic model to classify incoming packets into different flows and is used to provide a fair share of the bandwidth to all the flows using the queue. Each such flow is managed by the CoDel queuing discipline. Reordering within a flow is avoided since Codel internally uses a FIFO queue. PARAMETERS
limit has the same semantics as codel and is the hard limit on the real queue size. When this limit is reached, incoming packets are dropped. Default is 10240 packets. flows is the number of flows into which the incoming packets are classified. Due to the stochastic nature of hashing, multiple flows may end up being hashed into the same slot. Newer flows have priority over older ones. This parameter can be set only at load time since memory has to be allocated for the hash table. Default value is 1024. target has the same semantics as codel and is the acceptable minimum standing/persistent queue delay. This minimum delay is identified by tracking the local minimum queue delay that packets experience. Default value is 5ms. interval has the same semantics as codel and is used to ensure that the measured minimum delay does not become too stale. The minimum delay must be experienced in the last epoch of length .B interval. It should be set on the order of the worst-case RTT through the bottleneck to give endpoints sufficient time to react. Default value is 100ms. quantum is the number of bytes used as 'deficit' in the fair queuing algorithm. Default is set to 1514 bytes which corresponds to the Ethernet MTU plus the hardware header length of 14 bytes. ecn | noecn has the same semantics as codel and can be used to mark packets instead of dropping them. If ecn has been enabled, noecn can be used to turn it off and vice-a-versa. Unlike codel, ecn is turned on by default. EXAMPLES
#tc qdisc add dev eth0 root fq_codel #tc -s qdisc show qdisc fq_codel 8002: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms ecn Sent 428514 bytes 2269 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0 maxpacket 256 drop_overlimit 0 new_flow_count 0 ecn_mark 0 new_flows_len 0 old_flows_len 0 #tc qdisc add dev eth0 root fq_codel limit 2000 target 3ms interval 40ms noecn #tc -s qdisc show qdisc fq_codel 8003: dev eth0 root refcnt 2 limit 2000p flows 1024 quantum 1514 target 3.0ms interval 40.0ms Sent 2588985006 bytes 1783629 pkt (dropped 0, overlimits 0 requeues 34869) backlog 0b 0p requeues 34869 maxpacket 65226 drop_overlimit 0 new_flow_count 73 ecn_mark 0 new_flows_len 1 old_flows_len 3 SEE ALSO
tc(8), tc-codel(8), tc-red(8) AUTHORS
FQ_CoDel was implemented by Eric Dumazet. This manpage was written by Vijay Subramanian. Please report corrections to the Linux Networking mailing list <netdev@vger.kernel.org>. iproute2 4 June 2012 FQ_CoDel(8)
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