From 77879147a3481babffd7e368d977ab682545a6bd Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 19 Sep 2016 23:39:11 -0400 Subject: net_sched: sch_fq: add low_rate_threshold parameter This commit adds to the fq module a low_rate_threshold parameter to insert a delay after all packets if the socket requests a pacing rate below the threshold. This helps achieve more precise control of the sending rate with low-rate paths, especially policers. The basic issue is that if a congestion control module detects a policer at a certain rate, it may want fq to be able to shape to that policed rate. That way the sender can avoid policer drops by having the packets arrive at the policer at or just under the policed rate. The default threshold of 550Kbps was chosen analytically so that for policers or links at 500Kbps or 512Kbps fq would very likely invoke this mechanism, even if the pacing rate was briefly slightly above the available bandwidth. This value was then empirically validated with two years of production testing on YouTube video servers. Signed-off-by: Van Jacobson Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Nandita Dukkipati Signed-off-by: Eric Dumazet Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- include/uapi/linux/pkt_sched.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/uapi/linux/pkt_sched.h') diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h index 2382eed50278..f8e39dbaa781 100644 --- a/include/uapi/linux/pkt_sched.h +++ b/include/uapi/linux/pkt_sched.h @@ -792,6 +792,8 @@ enum { TCA_FQ_ORPHAN_MASK, /* mask applied to orphaned skb hashes */ + TCA_FQ_LOW_RATE_THRESHOLD, /* per packet delay under this rate */ + __TCA_FQ_MAX }; -- cgit v1.2.3 From fefa569a9d4bc4b7758c0fddd75bb0382c95da77 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 22 Sep 2016 08:58:55 -0700 Subject: net_sched: sch_fq: account for schedule/timers drifts It looks like the following patch can make FQ very precise, even in VM or stressed hosts. It matters at high pacing rates. We take into account the difference between the time that was programmed when last packet was sent, and current time (a drift of tens of usecs is often observed) Add an EWMA of the unthrottle latency to help diagnostics. This latency is the difference between current time and oldest packet in delayed RB-tree. This accounts for the high resolution timer latency, but can be different under stress, as fq_check_throttled() can be opportunistically be called from a dequeue() called after an enqueue() for a different flow. Tested: // Start a 10Gbit flow $ netperf --google-pacing-rate 1250000000 -H lpaa24 -l 10000 -- -K bbr & Before patch : $ sar -n DEV 10 5 | grep eth0 | grep Average Average: eth0 17106.04 756876.84 1102.75 1119049.02 0.00 0.00 0.52 After patch : $ sar -n DEV 10 5 | grep eth0 | grep Average Average: eth0 17867.00 800245.90 1151.77 1183172.12 0.00 0.00 0.52 A new iproute2 tc can output the 'unthrottle latency' : $ tc -s qd sh dev eth0 | grep latency 0 gc, 0 highprio, 32490767 throttled, 2382 ns latency Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/uapi/linux/pkt_sched.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/uapi/linux/pkt_sched.h') diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h index f8e39dbaa781..df7451d35131 100644 --- a/include/uapi/linux/pkt_sched.h +++ b/include/uapi/linux/pkt_sched.h @@ -811,7 +811,7 @@ struct tc_fq_qd_stats { __u32 flows; __u32 inactive_flows; __u32 throttled_flows; - __u32 pad; + __u32 unthrottle_latency_ns; }; /* Heavy-Hitter Filter */ -- cgit v1.2.3