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Date: Thu, 5 Jan 2012 10:08:05 -0800
From: Laurent Chavey <chavey@...gle.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>, Dave Taht <dave.taht@...il.com>
Subject: Re: [PATCH net-next] net_sched: sfq: extend limits
On Wed, Jan 4, 2012 at 4:18 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> SFQ as implemented in Linux is very limited, with at most 127 flows
> and limit of 127 packets. [ So if 127 flows are active, we have one
> packet per flow ]
>
> This patch brings to SFQ following features to cope with modern needs.
>
> - Ability to specify a smaller per flow limit of inflight packets.
> (default value being at 127 packets)
>
> - Ability to have up to 65408 active flows (instead of 127)
>
> - Ability to have head drops instead of tail drops
> (to drop old packets from a flow)
>
> Example of use : No more than 20 packets per flow, max 8000 flows, max
> 20000 packets in SFQ qdisc, hash table of 65536 slots.
>
> tc qdisc add ... sfq \
> flows 8000 \
> depth 20 \
> headdrop \
> limit 20000 \
> divisor 65536
>
> Ram usage :
>
> 2 bytes per hash table entry (instead of previous 1 byte/entry)
> 32 bytes per flow on 64bit arches, instead of 384 for QFQ, so much
> better cache hit ratio.
>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Dave Taht <dave.taht@...il.com>
> ---
> include/linux/pkt_sched.h | 16 +--
> net/sched/sch_sfq.c | 175 ++++++++++++++++++++++++------------
> 2 files changed, 124 insertions(+), 67 deletions(-)
>
> diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
> index 8daced3..8f1b928 100644
> --- a/include/linux/pkt_sched.h
> +++ b/include/linux/pkt_sched.h
> @@ -162,19 +162,17 @@ struct tc_sfq_qopt {
> unsigned flows; /* Maximal number of flows */
> };
>
> +struct tc_sfq_qopt_v1 {
> + struct tc_sfq_qopt v0;
> + unsigned int depth; /* max number of packets per flow */
> + unsigned int headdrop;
> +};
> +
> +
> struct tc_sfq_xstats {
> __s32 allot;
> };
>
> -/*
> - * NOTE: limit, divisor and flows are hardwired to code at the moment.
> - *
> - * limit=flows=128, divisor=1024;
> - *
> - * The only reason for this is efficiency, it is possible
> - * to change these parameters in compile time.
> - */
> -
> /* RED section */
>
> enum {
> diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> index 8430181..0a79640 100644
> --- a/net/sched/sch_sfq.c
> +++ b/net/sched/sch_sfq.c
> @@ -66,16 +66,18 @@
> SFQ is superior for this purpose.
>
> IMPLEMENTATION:
> - This implementation limits maximal queue length to 128;
> - max mtu to 2^18-1; max 128 flows, number of hash buckets to 1024.
> - The only goal of this restrictions was that all data
> - fit into one 4K page on 32bit arches.
> + This implementation limits :
> + - maximal queue length per flow to 127 packets.
> + - max mtu to 2^18-1;
> + - max 65408 flows,
> + - number of hash buckets to 65536.
>
> It is easy to increase these values, but not in flight. */
>
> -#define SFQ_DEPTH 128 /* max number of packets per flow */
> -#define SFQ_SLOTS 128 /* max number of flows */
> -#define SFQ_EMPTY_SLOT 255
> +#define SFQ_MAX_DEPTH 127 /* max number of packets per flow */
> +#define SFQ_DEFAULT_FLOWS 128
> +#define SFQ_MAX_FLOWS (0x10000 - SFQ_MAX_DEPTH - 1) /* max number of flows */
> +#define SFQ_EMPTY_SLOT 0xffff
> #define SFQ_DEFAULT_HASH_DIVISOR 1024
>
> /* We use 16 bits to store allot, and want to handle packets up to 64K
> @@ -84,13 +86,13 @@
> #define SFQ_ALLOT_SHIFT 3
> #define SFQ_ALLOT_SIZE(X) DIV_ROUND_UP(X, 1 << SFQ_ALLOT_SHIFT)
>
> -/* This type should contain at least SFQ_DEPTH + SFQ_SLOTS values */
> -typedef unsigned char sfq_index;
> +/* This type should contain at least SFQ_MAX_DEPTH + 1 + SFQ_MAX_FLOWS values */
> +typedef u16 sfq_index;
>
> /*
> * We dont use pointers to save space.
> - * Small indexes [0 ... SFQ_SLOTS - 1] are 'pointers' to slots[] array
> - * while following values [SFQ_SLOTS ... SFQ_SLOTS + SFQ_DEPTH - 1]
> + * Small indexes [0 ... SFQ_MAX_FLOWS - 1] are 'pointers' to slots[] array
> + * while following values [SFQ_MAX_FLOWS ... SFQ_MAX_FLOWS + SFQ_MAX_DEPTH]
> * are 'pointers' to dep[] array
> */
> struct sfq_head {
> @@ -102,28 +104,38 @@ struct sfq_slot {
> struct sk_buff *skblist_next;
> struct sk_buff *skblist_prev;
> sfq_index qlen; /* number of skbs in skblist */
> - sfq_index next; /* next slot in sfq chain */
> + sfq_index next; /* next slot in sfq RR chain */
> struct sfq_head dep; /* anchor in dep[] chains */
> unsigned short hash; /* hash value (index in ht[]) */
> short allot; /* credit for this slot */
> };
>
> struct sfq_sched_data {
> -/* Parameters */
> - int perturb_period;
> - unsigned int quantum; /* Allotment per round: MUST BE >= MTU */
> - int limit;
> +/* frequently used fields */
> + int limit; /* limit of total number of packets in this qdisc */
> unsigned int divisor; /* number of slots in hash table */
> -/* Variables */
> - struct tcf_proto *filter_list;
> - struct timer_list perturb_timer;
> + unsigned int maxflows; /* number of flows in flows array */
> + int headdrop;
> + int maxdepth; /* limit of packets per flow */
> +
> u32 perturbation;
> + struct tcf_proto *filter_list;
> sfq_index cur_depth; /* depth of longest slot */
> unsigned short scaled_quantum; /* SFQ_ALLOT_SIZE(quantum) */
> struct sfq_slot *tail; /* current slot in round */
> - sfq_index *ht; /* Hash table (divisor slots) */
> - struct sfq_slot slots[SFQ_SLOTS];
> - struct sfq_head dep[SFQ_DEPTH]; /* Linked list of slots, indexed by depth */
> + sfq_index *ht; /* Hash table ('divisor' slots) */
> + struct sfq_slot *slots; /* Flows table ('maxflows' entries) */
> +
> + struct sfq_head dep[SFQ_MAX_DEPTH + 1];
> + /* Linked lists of slots, indexed by depth
> + * dep[0] : list of unused flows
> + * dep[1] : list of flows with 1 packet
> + * dep[X] : list of flows with X packets
> + */
> +
> + int perturb_period;
> + unsigned int quantum; /* Allotment per round: MUST BE >= MTU */
> + struct timer_list perturb_timer;
> };
>
> /*
> @@ -131,9 +143,9 @@ struct sfq_sched_data {
> */
> static inline struct sfq_head *sfq_dep_head(struct sfq_sched_data *q, sfq_index val)
> {
> - if (val < SFQ_SLOTS)
why not use q->maxflows here rather than SFQ_MAX_FLOWS ?
looking at sfq_change(), q->maxflows may be <= to SFQ_MAX_FLOWS
the initial creation of the slots array in sfq_init() uses q->maxflows.
q->maxflows is initialized to SFQ_DEFAULT_FLOWS which is / maybe less
than SFQ_MAX_FLOWS
> + if (val < SFQ_MAX_FLOWS)
> return &q->slots[val].dep;
> - return &q->dep[val - SFQ_SLOTS];
> + return &q->dep[val - SFQ_MAX_FLOWS];
> }
>
> /*
> @@ -199,18 +211,19 @@ static unsigned int sfq_classify(struct sk_buff *skb, struct Qdisc *sch,
> }
>
> /*
> - * x : slot number [0 .. SFQ_SLOTS - 1]
> + * x : slot number [0 .. SFQ_MAX_FLOWS - 1]
> */
> static inline void sfq_link(struct sfq_sched_data *q, sfq_index x)
> {
> sfq_index p, n;
> - int qlen = q->slots[x].qlen;
> + struct sfq_slot *slot = &q->slots[x];
> + int qlen = slot->qlen;
>
> - p = qlen + SFQ_SLOTS;
> + p = qlen + SFQ_MAX_FLOWS;
> n = q->dep[qlen].next;
>
> - q->slots[x].dep.next = n;
> - q->slots[x].dep.prev = p;
> + slot->dep.next = n;
> + slot->dep.prev = p;
>
> q->dep[qlen].next = x; /* sfq_dep_head(q, p)->next = x */
> sfq_dep_head(q, n)->prev = x;
> @@ -275,6 +288,7 @@ static inline struct sk_buff *slot_dequeue_head(struct sfq_slot *slot)
>
> static inline void slot_queue_init(struct sfq_slot *slot)
> {
> + memset(slot, 0, sizeof(*slot));
> slot->skblist_prev = slot->skblist_next = (struct sk_buff *)slot;
> }
>
> @@ -305,7 +319,7 @@ static unsigned int sfq_drop(struct Qdisc *sch)
> x = q->dep[d].next;
> slot = &q->slots[x];
> drop:
> - skb = slot_dequeue_tail(slot);
> + skb = q->headdrop ? slot_dequeue_head(slot) : slot_dequeue_tail(slot);
> len = qdisc_pkt_len(skb);
> sfq_dec(q, x);
> kfree_skb(skb);
> @@ -349,16 +363,27 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> slot = &q->slots[x];
> if (x == SFQ_EMPTY_SLOT) {
> x = q->dep[0].next; /* get a free slot */
> + if (x >= SFQ_MAX_FLOWS)
> + return qdisc_drop(skb, sch);
> q->ht[hash] = x;
> slot = &q->slots[x];
> slot->hash = hash;
> }
>
> - /* If selected queue has length q->limit, do simple tail drop,
> - * i.e. drop _this_ packet.
> - */
> - if (slot->qlen >= q->limit)
> - return qdisc_drop(skb, sch);
> + if (slot->qlen >= q->maxdepth) {
> + struct sk_buff *head;
> +
> + if (!q->headdrop)
> + return qdisc_drop(skb, sch);
> +
> + head = slot_dequeue_head(slot);
> + sch->qstats.backlog -= qdisc_pkt_len(head);
> + qdisc_drop(head, sch);
> +
> + sch->qstats.backlog += qdisc_pkt_len(skb);
> + slot_queue_add(slot, skb);
> + return NET_XMIT_CN;
> + }
>
> sch->qstats.backlog += qdisc_pkt_len(skb);
> slot_queue_add(slot, skb);
> @@ -445,16 +470,18 @@ sfq_reset(struct Qdisc *sch)
> * We dont use sfq_dequeue()/sfq_enqueue() because we dont want to change
> * counters.
> */
> -static void sfq_rehash(struct sfq_sched_data *q)
> +static void sfq_rehash(struct Qdisc *sch)
> {
> + struct sfq_sched_data *q = qdisc_priv(sch);
> struct sk_buff *skb;
> int i;
> struct sfq_slot *slot;
> struct sk_buff_head list;
> + int dropped = 0;
>
> __skb_queue_head_init(&list);
>
> - for (i = 0; i < SFQ_SLOTS; i++) {
> + for (i = 0; i < q->maxflows; i++) {
> slot = &q->slots[i];
> if (!slot->qlen)
> continue;
> @@ -474,10 +501,18 @@ static void sfq_rehash(struct sfq_sched_data *q)
> slot = &q->slots[x];
> if (x == SFQ_EMPTY_SLOT) {
> x = q->dep[0].next; /* get a free slot */
> + if (x >= SFQ_MAX_FLOWS) {
> +drop: sch->qstats.backlog -= qdisc_pkt_len(skb);
> + kfree_skb(skb);
> + dropped++;
> + continue;
> + }
> q->ht[hash] = x;
> slot = &q->slots[x];
> slot->hash = hash;
> }
> + if (slot->qlen >= q->maxdepth)
> + goto drop;
> slot_queue_add(slot, skb);
> sfq_inc(q, x);
> if (slot->qlen == 1) { /* The flow is new */
> @@ -491,6 +526,8 @@ static void sfq_rehash(struct sfq_sched_data *q)
> slot->allot = q->scaled_quantum;
> }
> }
> + sch->q.qlen -= dropped;
> + qdisc_tree_decrease_qlen(sch, dropped);
> }
>
> static void sfq_perturbation(unsigned long arg)
> @@ -502,7 +539,7 @@ static void sfq_perturbation(unsigned long arg)
> spin_lock(root_lock);
> q->perturbation = net_random();
> if (!q->filter_list && q->tail)
> - sfq_rehash(q);
> + sfq_rehash(sch);
> spin_unlock(root_lock);
>
> if (q->perturb_period)
> @@ -513,23 +550,39 @@ static int sfq_change(struct Qdisc *sch, struct nlattr *opt)
> {
> struct sfq_sched_data *q = qdisc_priv(sch);
> struct tc_sfq_qopt *ctl = nla_data(opt);
> + struct tc_sfq_qopt_v1 *ctl_v1 = NULL;
> unsigned int qlen;
>
> if (opt->nla_len < nla_attr_size(sizeof(*ctl)))
> return -EINVAL;
> -
> + if (opt->nla_len >= nla_attr_size(sizeof(*ctl_v1)))
> + ctl_v1 = nla_data(opt);
> if (ctl->divisor &&
> (!is_power_of_2(ctl->divisor) || ctl->divisor > 65536))
> return -EINVAL;
>
> sch_tree_lock(sch);
> - q->quantum = ctl->quantum ? : psched_mtu(qdisc_dev(sch));
> - q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
> + if (ctl->quantum) {
> + q->quantum = ctl->quantum;
> + q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
> + }
> q->perturb_period = ctl->perturb_period * HZ;
> - if (ctl->limit)
> - q->limit = min_t(u32, ctl->limit, SFQ_DEPTH - 1);
> - if (ctl->divisor)
> + if (ctl->flows)
> + q->maxflows = min_t(u32, ctl->flows, SFQ_MAX_FLOWS);
> + if (ctl->divisor) {
> q->divisor = ctl->divisor;
> + q->maxflows = min_t(u32, q->maxflows, q->divisor);
> + }
> + if (ctl_v1) {
> + if (ctl_v1->depth)
> + q->maxdepth = min_t(u32, ctl_v1->depth, SFQ_MAX_DEPTH);
> + q->headdrop = ctl_v1->headdrop;
> + }
> + if (ctl->limit) {
> + q->limit = min_t(u32, ctl->limit, q->maxdepth * q->maxflows);
> + q->maxflows = min_t(u32, q->maxflows, q->limit);
> + }
> +
> qlen = sch->q.qlen;
> while (sch->q.qlen > q->limit)
> sfq_drop(sch);
> @@ -571,6 +624,7 @@ static void sfq_destroy(struct Qdisc *sch)
> q->perturb_period = 0;
> del_timer_sync(&q->perturb_timer);
> sfq_free(q->ht);
> + sfq_free(q->slots);
> }
>
> static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
> @@ -582,15 +636,17 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
> q->perturb_timer.data = (unsigned long)sch;
> init_timer_deferrable(&q->perturb_timer);
>
> - for (i = 0; i < SFQ_DEPTH; i++) {
> - q->dep[i].next = i + SFQ_SLOTS;
> - q->dep[i].prev = i + SFQ_SLOTS;
> + for (i = 0; i < SFQ_MAX_DEPTH + 1; i++) {
> + q->dep[i].next = i + SFQ_MAX_FLOWS;
> + q->dep[i].prev = i + SFQ_MAX_FLOWS;
> }
>
> - q->limit = SFQ_DEPTH - 1;
> + q->limit = SFQ_MAX_DEPTH;
> + q->maxdepth = SFQ_MAX_DEPTH;
> q->cur_depth = 0;
> q->tail = NULL;
> q->divisor = SFQ_DEFAULT_HASH_DIVISOR;
> + q->maxflows = SFQ_DEFAULT_FLOWS;
> q->quantum = psched_mtu(qdisc_dev(sch));
> q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
> q->perturb_period = 0;
> @@ -603,14 +659,15 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
> }
>
> q->ht = sfq_alloc(sizeof(q->ht[0]) * q->divisor);
> - if (!q->ht) {
> + q->slots = sfq_alloc(sizeof(q->slots[0]) * q->maxflows);
> + if (!q->ht || !q->slots) {
> sfq_destroy(sch);
> return -ENOMEM;
> }
> for (i = 0; i < q->divisor; i++)
> q->ht[i] = SFQ_EMPTY_SLOT;
>
> - for (i = 0; i < SFQ_SLOTS; i++) {
> + for (i = 0; i < q->maxflows; i++) {
> slot_queue_init(&q->slots[i]);
> sfq_link(q, i);
> }
> @@ -625,14 +682,16 @@ static int sfq_dump(struct Qdisc *sch, struct sk_buff *skb)
> {
> struct sfq_sched_data *q = qdisc_priv(sch);
> unsigned char *b = skb_tail_pointer(skb);
> - struct tc_sfq_qopt opt;
> -
> - opt.quantum = q->quantum;
> - opt.perturb_period = q->perturb_period / HZ;
> -
> - opt.limit = q->limit;
> - opt.divisor = q->divisor;
> - opt.flows = q->limit;
> + struct tc_sfq_qopt_v1 opt;
> +
> + memset(&opt, 0, sizeof(opt));
> + opt.v0.quantum = q->quantum;
> + opt.v0.perturb_period = q->perturb_period / HZ;
> + opt.v0.limit = q->limit;
> + opt.v0.divisor = q->divisor;
> + opt.v0.flows = q->maxflows;
> + opt.depth = q->maxdepth;
> + opt.headdrop = q->headdrop;
>
> NLA_PUT(skb, TCA_OPTIONS, sizeof(opt), &opt);
>
>
>
> --
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