Add TCA_FQ_CODEL_CE_THRESHOLD_ECT1 boolean option to select Low Latency,
Low Loss, Scalable Throughput (L4S) style marking, along with ce_threshold.
If enabled, only packets with ECT(1) can be transformed to CE
if their sojourn time is above the ce_threshold.
Note that this new option does not change rules for codel law.
In particular, if TCA_FQ_CODEL_ECN is left enabled (this is
the default when fq_codel qdisc is created), ECT(0) packets can
still get CE if codel law (as governed by limit/target) decides so.
Section 4.3.b of current draft [1] states:
b. A scheduler with per-flow queues such as FQ-CoDel or FQ-PIE can
be used for L4S. For instance within each queue of an FQ-CoDel
system, as well as a CoDel AQM, there is typically also ECN
marking at an immediate (unsmoothed) shallow threshold to support
use in data centres (see Sec.5.2.7 of [RFC8290]). This can be
modified so that the shallow threshold is solely applied to
ECT(1) packets. Then if there is a flow of non-ECN or ECT(0)
packets in the per-flow-queue, the Classic AQM (e.g. CoDel) is
applied; while if there is a flow of ECT(1) packets in the queue,
the shallower (typically sub-millisecond) threshold is applied.
Tested:
tc qd replace dev eth1 root fq_codel ce_threshold_ect1 50usec
netperf ... -t TCP_STREAM -- K dctcp
tc -s -d qd sh dev eth1
qdisc fq_codel 8022: root refcnt 32 limit 10240p flows 1024 quantum 9212 target 5ms ce_threshold_ect1 49us interval 100ms memory_limit 32Mb ecn drop_batch 64
Sent 14388596616 bytes 9543449 pkt (dropped 0, overlimits 0 requeues 152013)
backlog 0b 0p requeues 152013
maxpacket 68130 drop_overlimit 0 new_flow_count 95678 ecn_mark 0 ce_mark 7639
new_flows_len 0 old_flows_len 0
[1] L4S current draft:
https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-l4s-arch
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Cc: Tom Henderson <tomh@tomh.org>
Cc: Bob Briscoe <in@bobbriscoe.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
e72aeb9ee0