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Date: Tue, 02 Apr 2019 19:25:57 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Gautam Ramakrishnan <gautamramk@...il.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, davem@...emloft.net,
netdev@...r.kernel.org,
"Mohit P . Tahiliani" <tahiliani@...k.edu.in>,
"Sachin D . Patil" <sdp.sachin@...il.com>,
Mohit Bhasi <mohitbhasi1998@...il.com>,
"V . Saicharan" <vsaicharan1998@...il.com>,
Leslie Monis <lesliemonis@...il.com>,
Dave Taht <dave.taht@...il.com>
Subject: Re: [RFC net-next 2/2] net: sched: fq_pie: Flow Queue PIE AQM
Gautam Ramakrishnan <gautamramk@...il.com> writes:
> Hello, thanks for the feedback
>
> On Tue, Apr 2, 2019 at 4:19 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> Some suggestions below to make fq_pie and fq_codel more similar (ref. my
>> previous email).
>>
>> Also, a few unrelated nits.
>>
>> > From: Mohit P. Tahiliani <tahiliani@...k.edu.in>
>> >
>> > FQ-PIE incorporates fair/flow queuing in which every queue
>> > is managed by an instance of PIE queueing discipline.
>> > The algorithm provides good control over the queueing delay
>> > while at the same time, ensures fairness across various
>> > flows sharing the same link.
>> >
>> > Principles:
>> > - Packets are classified stochastically on flows.
>> > - Each flow has a PIE managed queue.
>> > - Flows are linked onto two (Round Robin) lists,
>> > so that new flows have priority on old ones.
>> > - For a given flow, packets are dropped on arrival according
>> > to a drop probability.
>> > - Tail drops only.
>>
>> Why tail drops only?
>
> I had mentioned this because packets are dropped only at enqueue.
Yup, realise that; was just wondering why you went with this design
instead of doing the head drop that fq_codel does?
>>
>> > Usage:
>> > tc qdisc ... fq_pie [ limit PACKETS ] [ flows NUMBER ]
>> > [ alpha NUMBER ] [ beta NUMBER ]
>> > [ target TIME us ] [ tupdate TIME us ]
>> > [ bytemode ] [ quantum BYTES ]
>> > [ ecn | ecn_prob PERCENTAGE ]
>> >
>> > defaults: 1024 flows, 10240 packets limit, quantum : device MTU
>> > target: 15ms
>> > tupdate: 15ms
>> > alpha: 2 (on a scale of 0 to 16)
>> > beta: 20 (on a scale of 0 to 16)
>> > ecn: false
>> > ecn_prob: 10%
>> >
>> > Signed-off-by: Mohit P. Tahiliani <tahiliani@...k.edu.in>
>> > Signed-off-by: Sachin D. Patil <sdp.sachin@...il.com>
>> > Signed-off-by: Mohit Bhasi <mohitbhasi1998@...il.com>
>> > Signed-off-by: V. Saicharan <vsaicharan1998@...il.com>
>> > Signed-off-by: Leslie Monis <lesliemonis@...il.com>
>> > Signed-off-by: Gautam Ramakrishnan <gautamramk@...il.com>
>> > Cc: Dave Taht <dave.taht@...il.com>
>> > ---
>> > include/uapi/linux/pkt_sched.h | 28 ++
>> > net/sched/Kconfig | 14 +-
>> > net/sched/Makefile | 1 +
>> > net/sched/sch_fq_pie.c | 485 +++++++++++++++++++++++++++++++++
>> > 4 files changed, 527 insertions(+), 1 deletion(-)
>> > create mode 100644 net/sched/sch_fq_pie.c
>> >
>> > diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
>> > index 7ee74c3474bf..005413bd09ee 100644
>> > --- a/include/uapi/linux/pkt_sched.h
>> > +++ b/include/uapi/linux/pkt_sched.h
>> > @@ -964,6 +964,34 @@ struct tc_pie_xstats {
>> > __u32 ecn_mark; /* packets marked with ecn*/
>> > };
>> >
>> > +/* FQ PIE */
>> > +enum {
>> > + TCA_FQ_PIE_UNSPEC,
>> > + TCA_FQ_PIE_TARGET,
>> > + TCA_FQ_PIE_LIMIT,
>> > + TCA_FQ_PIE_TUPDATE,
>> > + TCA_FQ_PIE_ALPHA,
>> > + TCA_FQ_PIE_BETA,
>> > + TCA_FQ_PIE_ECN,
>> > + TCA_FQ_PIE_QUANTUM,
>> > + TCA_FQ_PIE_BYTEMODE,
>> > + TCA_FQ_PIE_FLOWS,
>> > + TCA_FQ_PIE_ECN_PROB,
>> > + __TCA_FQ_PIE_MAX
>> > +};
>> > +#define TCA_FQ_PIE_MAX (__TCA_FQ_PIE_MAX - 1)
>> > +
>> > +struct tc_fq_pie_xstats {
>> > + __u32 packets_in; /* total number of packets enqueued */
>> > + __u32 dropped; /* packets dropped due to fq_pie_action */
>> > + __u32 overlimit; /* dropped due to lack of space in queue */
>> > + __u32 ecn_mark; /* packets marked with ecn*/
>> > + __u32 new_flow_count; /* number of time packets
>> > + created a 'new flow' */
>> > + __u32 new_flows_len; /* count of flows in new list */
>> > + __u32 old_flows_len; /* count of flows in old list */
>> > +};
>> > +
>> > /* CBS */
>> > struct tc_cbs_qopt {
>> > __u8 offload;
>> > diff --git a/net/sched/Kconfig b/net/sched/Kconfig
>> > index 5c02ad97ef23..49f4dd9894a0 100644
>> > --- a/net/sched/Kconfig
>> > +++ b/net/sched/Kconfig
>> > @@ -358,13 +358,25 @@ config NET_SCH_PIE
>> > help
>> > Say Y here if you want to use the Proportional Integral controller
>> > Enhanced scheduler packet scheduling algorithm.
>> > - For more information, please see https://tools.ietf.org/html/rfc8033
>> > + For more information, please see
>> > + http://tools.ietf.org/html/draft-pan-tsvwg-pie-00
>> >
>> > To compile this driver as a module, choose M here: the module
>> > will be called sch_pie.
>> >
>> > If unsure, say N.
>> >
>> > +config NET_SCH_FQ_PIE
>> > + tristate "Flow Queue Proportional Integral controller Enhanced (FQ-PIE) scheduler"
>> > + help
>> > + Say Y here if you want to use the Flow Queue Proportional Integral controller
>> > + Enhanced scheduler packet scheduling algorithm.
>> > +
>> > + To compile this driver as a module, choose M here: the module
>> > + will be called sch_fq_pie.
>> > +
>> > + If unsure, say N.
>> > +
>> > config NET_SCH_INGRESS
>> > tristate "Ingress/classifier-action Qdisc"
>> > depends on NET_CLS_ACT
>> > diff --git a/net/sched/Makefile b/net/sched/Makefile
>> > index 8a40431d7b5c..fdcd3f7b2fb2 100644
>> > --- a/net/sched/Makefile
>> > +++ b/net/sched/Makefile
>> > @@ -55,6 +55,7 @@ obj-$(CONFIG_NET_SCH_CAKE) += sch_cake.o
>> > obj-$(CONFIG_NET_SCH_FQ) += sch_fq.o
>> > obj-$(CONFIG_NET_SCH_HHF) += sch_hhf.o
>> > obj-$(CONFIG_NET_SCH_PIE) += sch_pie.o
>> > +obj-$(CONFIG_NET_SCH_FQ_PIE) += sch_fq_pie.o
>> > obj-$(CONFIG_NET_SCH_CBS) += sch_cbs.o
>> > obj-$(CONFIG_NET_SCH_ETF) += sch_etf.o
>> > obj-$(CONFIG_NET_SCH_TAPRIO) += sch_taprio.o
>> > diff --git a/net/sched/sch_fq_pie.c b/net/sched/sch_fq_pie.c
>> > new file mode 100644
>> > index 000000000000..4ccefa0bc7f0
>> > --- /dev/null
>> > +++ b/net/sched/sch_fq_pie.c
>> > @@ -0,0 +1,485 @@
>> > +/*
>> > + * net/sched/sch_fq_pie.c
>> > + *
>> > + * This program is free software; you can redistribute it and/or
>> > + * modify it under the terms of the GNU General Public License
>> > + * as published by the Free Software Foundation; either version 2
>> > + * of the License.
>> > + *
>> > + * This program is distributed in the hope that it will be useful,
>> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> > + * GNU General Public License for more details.
>>
>> Lose the license boilerplate and replace it with a SPDX header line.
>
> I shall do that.
>
>>
>> > + * Author: Mohit P. Tahiliani <tahiliani@...k.edu.in>
>> > + * Author: Sachin D. Patil <sdp.sachin@...il.com>
>> > + * Author: Mohit Bhasi <mohitbhasi1998@...il.com>
>> > + * Author: V Saicharan <vsaicharan1998@...il.com>
>> > + * Author: Leslie Monis <lesliemonis@...il.com>
>> > + * Author: Gautam Ramakrishnan <gautamramk@...il.com>
>> > + *
>> > + * References:
>> > + * RFC 8033: https://tools.ietf.org/html/rfc8033
>> > + */
>> > +
>> > +#include <linux/jhash.h>
>> > +#include <linux/vmalloc.h>
>> > +#include <net/pie.h>
>> > +
>> > +struct fq_pie_params {
>> > + struct pie_params p_params;
>> > + u32 ecn_prob;
>> > + u32 flows_cnt;
>> > +};
>> > +
>> > +struct fq_pie_stats {
>> > + u32 packets_in; /* total number of packets enqueued */
>> > + u32 dropped; /* packets dropped due to fq_pie action */
>> > + u32 overlimit; /* dropped due to lack of space in queue */
>> > + u32 ecn_mark; /* packets marked with ECN */
>> > + u32 new_flow_count; /* number of time packets created a new flow */
>> > +};
>> > +
>> > +struct fq_pie_flow {
>> > + s32 deficit; /* number of credits remaining for the flow */
>> > + u32 backlog; /* size of data in the flow */
>> > + u32 qlen; /* number of packets in the flow */
>> > + struct sk_buff *head;
>> > + struct sk_buff *tail;
>> > + struct list_head flowchain;
>> > + struct pie_vars vars; /* pie vars for the flow */
>> > + struct pie_stats stats; /* pie stats for the flow */
>> > +};
>> > +
>> > +struct fq_pie_sched_data {
>> > + u32 quantum; /* number of credits in deficit round robin */
>> > + struct fq_pie_flow *flows;
>> > + struct Qdisc *sch;
>> > + struct fq_pie_params params;
>> > + struct fq_pie_stats stats;
>> > + struct list_head old_flows;
>> > + struct list_head new_flows;
>> > + struct timer_list adapt_timer;
>> > +};
>>
>> The flow and sched_data structs have quite a bit in common with those in
>> fq_codel; but the members are in a different order.
>>
>> > +static void fq_pie_params_init(struct fq_pie_params *params)
>> > +{
>> > + pie_params_init(¶ms->p_params);
>> > + params->ecn_prob = 10;
>> > + params->flows_cnt = 1024;
>> > +}
>> > +
>> > +static inline void flow_queue_add(struct fq_pie_flow *flow,
>> > + struct sk_buff *skb)
>> > +{
>> > + if (!flow->head)
>> > + flow->head = skb;
>> > + else
>> > + flow->tail->next = skb;
>> > + flow->tail = skb;
>> > + skb->next = NULL;
>> > +}
>> > +
>> > +static int fq_pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>> > + struct sk_buff **to_free)
>> > +{
>> > + struct fq_pie_sched_data *q = qdisc_priv(sch);
>> > + struct fq_pie_flow *sel_flow;
>> > + u32 pkt_len;
>> > + u32 idx;
>> > + u8 enqueue = false;
>> > +
>> > + /* Classifies packet into corresponding flow */
>> > + idx = reciprocal_scale(skb_get_hash(skb), q->params.flows_cnt);
>> > + sel_flow = &q->flows[idx];
>>
>> This is missing the ability to override the classification from tc
>> filters. See fq_codel_classify().
>
> I wanted to keep it simple initially. Shall add that.
>
>>
>> > +
>> > + /* Checks if the qdisc is full */
>> > + if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
>> > + q->stats.overlimit++;
>> > + sel_flow->stats.overlimit++;
>> > + goto out;
>> > + }
>>
>> The memory_limit checks in fq_codel have turned out to be quite useful
>> on constrained systems. I'd suggest adding them here as well.
>
> I shall add that too.
>
>>
>> > +
>> > + if (!drop_early(sch, sel_flow->backlog, skb->len, &sel_flow->vars,
>> > + &q->params.p_params)) {
>> > + enqueue = true;
>> > + } else if (q->params.p_params.ecn &&
>> > + sel_flow->vars.prob <=
>> > + (MAX_PROB / 100) * q->params.ecn_prob &&
>> > + INET_ECN_set_ce(skb)) {
>> > + /* If packet is ecn capable, mark it if drop probability
>> > + * is lower than the parameter ecn_prob, else drop it.
>> > + */
>> > + q->stats.ecn_mark++;
>> > + sel_flow->stats.ecn_mark++;
>> > + enqueue = true;
>> > + }
>> > + if (enqueue) {
>> > + pkt_len = qdisc_pkt_len(skb);
>> > + q->stats.packets_in++;
>> > + sch->qstats.backlog += pkt_len;
>> > + sch->q.qlen++;
>> > + flow_queue_add(sel_flow, skb);
>> > + if (list_empty(&sel_flow->flowchain)) {
>> > + list_add_tail(&sel_flow->flowchain, &q->new_flows);
>> > + q->stats.new_flow_count++;
>> > + sel_flow->deficit = q->quantum;
>> > + sel_flow->stats.dropped = 0;
>> > + sel_flow->qlen = 0;
>> > + sel_flow->backlog = 0;
>> > + }
>> > + sel_flow->qlen++;
>> > + sel_flow->stats.packets_in++;
>> > + sel_flow->backlog += pkt_len;
>> > + return NET_XMIT_SUCCESS;
>> > + }
>> > +out:
>> > + q->stats.dropped++;
>> > + sel_flow->stats.dropped++;
>> > + return qdisc_drop(skb, sch, to_free);
>>
>> You probably want to return NET_XMIT_CN instead of NET_XMIT_DROP here.
>>
>
> Should I replace qdisc_drop with __qdisc_drop and return NET_XMIT_CN?
Yeah, I think that would be more appropriate here, as that would
directly throttle sockets on the same host.
>> > +}
>> > +
>> > +static const struct nla_policy fq_pie_policy[TCA_FQ_PIE_MAX + 1] = {
>> > + [TCA_FQ_PIE_TARGET] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_LIMIT] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_TUPDATE] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_ALPHA] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_BETA] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_ECN] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_QUANTUM] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_BYTEMODE] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_FLOWS] = {.type = NLA_U32},
>> > + [TCA_FQ_PIE_ECN_PROB] = {.type = NLA_U32}
>> > +};
>> > +
>> > +static inline struct sk_buff *dequeue_head(struct fq_pie_flow *flow)
>> > +{
>> > + struct sk_buff *skb = flow->head;
>> > +
>> > + flow->head = skb->next;
>> > + skb->next = NULL;
>> > + return skb;
>> > +}
>> > +
>> > +static struct sk_buff *fq_pie_qdisc_dequeue(struct Qdisc *sch)
>> > +{
>> > + struct fq_pie_sched_data *q = qdisc_priv(sch);
>> > + struct sk_buff *skb = NULL;
>> > + struct fq_pie_flow *flow;
>> > + struct list_head *head;
>> > + u32 pkt_len;
>> > +
>> > +begin:
>> > + head = &q->new_flows;
>> > + if (list_empty(head)) {
>> > + head = &q->old_flows;
>> > + if (list_empty(head))
>> > + return NULL;
>> > + }
>> > +
>> > + flow = list_first_entry(head, struct fq_pie_flow, flowchain);
>> > + /* Flow has exhausted all its credits */
>> > + if (flow->deficit <= 0) {
>> > + flow->deficit += q->quantum;
>> > + list_move_tail(&flow->flowchain, &q->old_flows);
>> > + goto begin;
>> > + }
>> > +
>> > + if (flow->head) {
>> > + skb = dequeue_head(flow);
>> > + pkt_len = qdisc_pkt_len(skb);
>> > + sch->qstats.backlog -= pkt_len;
>> > + sch->q.qlen--;
>> > + qdisc_bstats_update(sch, skb);
>> > + }
>>
>> If you factor this out into a dequeue_func(), this dequeue() function is
>> very close to identical to the one in fq_codel().
>
> Do you suggest I put the if(flow->head) block in a different function?
Yeah, that was what I meant. However, without doing the full refactoring
it's only borderline useful, so feel free to just keep it the way it
is...
-Toke
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