[PATCH v3 net-next-2.6] net_sched: sch_sfq: better struct layouts

Eric Dumazet
2010-12-20T22:55:08Z

Here is a respin of patch.

I'll send a short patch to make SFQ more fair in presence of large
packets as well.

Thanks

[PATCH v3 net-next-2.6] net_sched: sch_sfq: better struct layouts

This patch shrinks sizeof(struct sfq_sched_data)
from 0x14f8 (or more if spinlocks are bigger) to 0x1180 bytes, and
reduce text size as well.

text data bss dec hex filename
4821 152 0 4973 136d old/net/sched/sch_sfq.o
4627 136 0 4763 129b new/net/sched/sch_sfq.o

All data for a slot/flow is now grouped in a compact and cache friendly
structure, instead of being spreaded in many different points.

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 */
struct sfq_head dep; /* anchor in dep[] chains */
unsigned short hash; /* hash value (index in ht[]) */
short allot; /* credit for this slot */
};

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Jarek Poplawski <jarkao2@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
---
v3: respin after two prior patches applied

net/sched/sch_sfq.c | 260 ++++++++++++++++++++++++++----------------
1 file changed, 162 insertions(+), 98 deletions(-)

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 42396c9..c474b4b 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -67,27 +67,42 @@

IMPLEMENTATION:
This implementation limits maximal queue length to 128;
- maximal mtu to 2^15-1; number of hash buckets to 1024.
+ maximal mtu to 2^15-1; max 128 flows, number of hash buckets to 1024.
The only goal of this restrictions was that all data
- fit into one 4K page :-). Struct sfq_sched_data is
- organized in anti-cache manner: all the data for a bucket
- are scattered over different locations. This is not good,
- but it allowed me to put it into 4K.
+ fit into one 4K page on 32bit arches.

It is easy to increase these values, but not in flight. */

-#define SFQ_DEPTH 128
+#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_HASH_DIVISOR 1024

-/* This type should contain at least SFQ_DEPTH*2 values */
+/* This type should contain at least SFQ_DEPTH + SFQ_SLOTS values */
typedef unsigned char 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]
+ * are 'pointers' to dep[] array
+ */
struct sfq_head
{
sfq_index next;
sfq_index prev;
};

+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 */
+ 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 */
@@ -99,17 +114,24 @@ struct sfq_sched_data
struct tcf_proto *filter_list;
struct timer_list perturb_timer;
u32 perturbation;
- sfq_index tail; /* Index of current slot in round */
- sfq_index max_depth; /* Maximal depth */
+ sfq_index cur_depth; /* depth of longest slot */

+ struct sfq_slot *tail; /* current slot in round */
sfq_index ht[SFQ_HASH_DIVISOR]; /* Hash table */
- sfq_index next[SFQ_DEPTH]; /* Active slots link */
- short allot[SFQ_DEPTH]; /* Current allotment per slot */
- unsigned short hash[SFQ_DEPTH]; /* Hash value indexed by slots */
- struct sk_buff_head qs[SFQ_DEPTH]; /* Slot queue */
- struct sfq_head dep[SFQ_DEPTH*2]; /* Linked list of slots, indexed by depth */
+ struct sfq_slot slots[SFQ_SLOTS];
+ struct sfq_head dep[SFQ_DEPTH]; /* Linked list of slots, indexed by depth */
};

+/*
+ * sfq_head are either in a sfq_slot or in dep[] array
+ */
+static inline struct sfq_head *sfq_dep_head(struct sfq_sched_data *q, sfq_index val)
+{
+ if (val < SFQ_SLOTS)
+ return &q->slots[val].dep;
+ return &q->dep[val - SFQ_SLOTS];
+}
+
static __inline__ unsigned sfq_fold_hash(struct sfq_sched_data *q, u32 h, u32 h1)
{
return jhash_2words(h, h1, q->perturbation) & (SFQ_HASH_DIVISOR - 1);
@@ -200,30 +222,41 @@ static unsigned int sfq_classify(struct sk_buff *skb, struct Qdisc *sch,
return 0;
}

+/*
+ * x : slot number [0 .. SFQ_SLOTS - 1]
+ */
static inline void sfq_link(struct sfq_sched_data *q, sfq_index x)
{
sfq_index p, n;
- int d = q->qs[x].qlen + SFQ_DEPTH;
+ int qlen = q->slots[x].qlen;

- p = d;
- n = q->dep[d].next;
- q->dep[x].next = n;
- q->dep[x].prev = p;
- q->dep[p].next = q->dep[n].prev = x;
+ p = qlen + SFQ_SLOTS;
+ n = q->dep[qlen].next;
+
+ q->slots[x].dep.next = n;
+ q->slots[x].dep.prev = p;
+
+ q->dep[qlen].next = x; /* sfq_dep_head(q, p)->next = x */
+ sfq_dep_head(q, n)->prev = x;
}

+#define sfq_unlink(q, x, n, p) \
+ n = q->slots[x].dep.next; \
+ p = q->slots[x].dep.prev; \
+ sfq_dep_head(q, p)->next = n; \
+ sfq_dep_head(q, n)->prev = p
+
+
static inline void sfq_dec(struct sfq_sched_data *q, sfq_index x)
{
sfq_index p, n;
+ int d;

- n = q->dep[x].next;
- p = q->dep[x].prev;
- q->dep[p].next = n;
- q->dep[n].prev = p;
-
- if (n == p && q->max_depth == q->qs[x].qlen + 1)
- q->max_depth--;
+ sfq_unlink(q, x, n, p);

+ d = q->slots[x].qlen--;
+ if (n == p && q->cur_depth == d)
+ q->cur_depth--;
sfq_link(q, x);
}

@@ -232,34 +265,72 @@ static inline void sfq_inc(struct sfq_sched_data *q, sfq_index x)
sfq_index p, n;
int d;

- n = q->dep[x].next;
- p = q->dep[x].prev;
- q->dep[p].next = n;
- q->dep[n].prev = p;
- d = q->qs[x].qlen;
- if (q->max_depth < d)
- q->max_depth = d;
+ sfq_unlink(q, x, n, p);

+ d = ++q->slots[x].qlen;
+ if (q->cur_depth < d)
+ q->cur_depth = d;
sfq_link(q, x);
}

+/* helper functions : might be changed when/if skb use a standard list_head */
+
+/* remove one skb from tail of slot queue */
+static inline struct sk_buff *slot_dequeue_tail(struct sfq_slot *slot)
+{
+ struct sk_buff *skb = slot->skblist_prev;
+
+ slot->skblist_prev = skb->prev;
+ skb->next = skb->prev = NULL;
+ return skb;
+}
+
+/* remove one skb from head of slot queue */
+static inline struct sk_buff *slot_dequeue_head(struct sfq_slot *slot)
+{
+ struct sk_buff *skb = slot->skblist_next;
+
+ slot->skblist_next = skb->next;
+ skb->next = skb->prev = NULL;
+ return skb;
+}
+
+static inline void slot_queue_init(struct sfq_slot *slot)
+{
+ slot->skblist_prev = slot->skblist_next = (struct sk_buff *)slot;
+}
+
+/* add skb to slot queue (tail add) */
+static inline void slot_queue_add(struct sfq_slot *slot, struct sk_buff *skb)
+{
+ skb->prev = slot->skblist_prev;
+ skb->next = (struct sk_buff *)slot;
+ slot->skblist_prev->next = skb;
+ slot->skblist_prev = skb;
+}
+
+#define slot_queue_walk(slot, skb) \
+ for (skb = slot->skblist_next; \
+ skb != (struct sk_buff *)slot; \
+ skb = skb->next)
+
static unsigned int sfq_drop(struct Qdisc *sch)
{
struct sfq_sched_data *q = qdisc_priv(sch);
- sfq_index d = q->max_depth;
+ sfq_index x, d = q->cur_depth;
struct sk_buff *skb;
unsigned int len;
+ struct sfq_slot *slot;

- /* Queue is full! Find the longest slot and
- drop a packet from it */
-
+ /* Queue is full! Find the longest slot and drop tail packet from it */
if (d > 1) {
- sfq_index x = q->dep[d + SFQ_DEPTH].next;
- skb = q->qs[x].prev;
+ x = q->dep[d].next;
+ slot = &q->slots[x];
+drop:
+ skb = slot_dequeue_tail(slot);
len = qdisc_pkt_len(skb);
- __skb_unlink(skb, &q->qs[x]);
- kfree_skb(skb);
sfq_dec(q, x);
+ kfree_skb(skb);
sch->q.qlen--;
sch->qstats.drops++;
sch->qstats.backlog -= len;
@@ -268,18 +339,11 @@ static unsigned int sfq_drop(struct Qdisc *sch)

if (d == 1) {
/* It is difficult to believe, but ALL THE SLOTS HAVE LENGTH 1. */
- d = q->next[q->tail];
- q->next[q->tail] = q->next[d];
- skb = q->qs[d].prev;
- len = qdisc_pkt_len(skb);
- __skb_unlink(skb, &q->qs[d]);
- kfree_skb(skb);
- sfq_dec(q, d);
- sch->q.qlen--;
- q->ht[q->hash[d]] = SFQ_DEPTH;
- sch->qstats.drops++;
- sch->qstats.backlog -= len;
- return len;
+ x = q->tail->next;
+ slot = &q->slots[x];
+ q->tail->next = slot->next;
+ q->ht[slot->hash] = SFQ_EMPTY_SLOT;
+ goto drop;
}

return 0;
@@ -291,6 +355,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
struct sfq_sched_data *q = qdisc_priv(sch);
unsigned int hash;
sfq_index x;
+ struct sfq_slot *slot;
int uninitialized_var(ret);

hash = sfq_classify(skb, sch, &ret);
@@ -303,30 +368,33 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
hash--;

x = q->ht[hash];
- if (x == SFQ_DEPTH) {
- q->ht[hash] = x = q->dep[SFQ_DEPTH].next;
- q->hash[x] = hash;
+ slot = &q->slots[x];
+ if (x == SFQ_EMPTY_SLOT) {
+ x = q->dep[0].next; /* get a free slot */
+ q->ht[hash] = x;
+ slot = &q->slots[x];
+ slot->hash = hash;
+ slot_queue_init(slot);
}

- /* If selected queue has length q->limit, this means that
- * all another queues are empty and that we do simple tail drop,
+ /* If selected queue has length q->limit, do simple tail drop,
* i.e. drop _this_ packet.
*/
- if (q->qs[x].qlen >= q->limit)
+ if (slot->qlen >= q->limit)
return qdisc_drop(skb, sch);

sch->qstats.backlog += qdisc_pkt_len(skb);
- __skb_queue_tail(&q->qs[x], skb);
+ slot_queue_add(slot, skb);
sfq_inc(q, x);
- if (q->qs[x].qlen == 1) { /* The flow is new */
- if (q->tail == SFQ_DEPTH) { /* It is the first flow */
- q->next[x] = x;
+ if (slot->qlen == 1) { /* The flow is new */
+ if (q->tail == NULL) { /* It is the first flow */
+ slot->next = x;
} else {
- q->next[x] = q->next[q->tail];
- q->next[q->tail] = x;
+ slot->next = q->tail->next;
+ q->tail->next = x;
}
- q->tail = x;
- q->allot[x] = q->quantum;
+ q->tail = slot;
+ slot->allot = q->quantum;
}
if (++sch->q.qlen <= q->limit) {
sch->bstats.bytes += qdisc_pkt_len(skb);
@@ -342,14 +410,12 @@ static struct sk_buff *
sfq_peek(struct Qdisc *sch)
{
struct sfq_sched_data *q = qdisc_priv(sch);
- sfq_index a;

/* No active slots */
- if (q->tail == SFQ_DEPTH)
+ if (q->tail == NULL)
return NULL;

- a = q->next[q->tail];
- return skb_peek(&q->qs[a]);
+ return q->slots[q->tail->next].skblist_next;
}

static struct sk_buff *
@@ -358,31 +424,31 @@ sfq_dequeue(struct Qdisc *sch)
struct sfq_sched_data *q = qdisc_priv(sch);
struct sk_buff *skb;
sfq_index a, next_a;
+ struct sfq_slot *slot;

/* No active slots */
- if (q->tail == SFQ_DEPTH)
+ if (q->tail == NULL)
return NULL;

- a = q->next[q->tail];
-
- /* Grab packet */
- skb = __skb_dequeue(&q->qs[a]);
+ a = q->tail->next;
+ slot = &q->slots[a];
+ skb = slot_dequeue_head(slot);
sfq_dec(q, a);
sch->q.qlen--;
sch->qstats.backlog -= qdisc_pkt_len(skb);

/* Is the slot empty? */
- if (q->qs[a].qlen == 0) {
- q->ht[q->hash[a]] = SFQ_DEPTH;
- next_a = q->next[a];
+ if (slot->qlen == 0) {
+ q->ht[slot->hash] = SFQ_EMPTY_SLOT;
+ next_a = slot->next;
if (a == next_a) {
- q->tail = SFQ_DEPTH;
+ q->tail = NULL; /* no more active slots */
return skb;
}
- q->next[q->tail] = next_a;
- } else if ((q->allot[a] -= qdisc_pkt_len(skb)) <= 0) {
- q->allot[a] += q->quantum;
- q->tail = a;
+ q->tail->next = next_a;
+ } else if ((slot->allot -= qdisc_pkt_len(skb)) <= 0) {
+ q->tail = slot;
+ slot->allot += q->quantum;
}
return skb;
}
@@ -446,17 +512,16 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
init_timer_deferrable(&q->perturb_timer);

for (i = 0; i < SFQ_HASH_DIVISOR; i++)
- q->ht[i] = SFQ_DEPTH;
+ q->ht[i] = SFQ_EMPTY_SLOT;

for (i = 0; i < SFQ_DEPTH; i++) {
- skb_queue_head_init(&q->qs[i]);
- q->dep[i + SFQ_DEPTH].next = i + SFQ_DEPTH;
- q->dep[i + SFQ_DEPTH].prev = i + SFQ_DEPTH;
+ q->dep[i].next = i + SFQ_SLOTS;
+ q->dep[i].prev = i + SFQ_SLOTS;
}

q->limit = SFQ_DEPTH - 1;
- q->max_depth = 0;
- q->tail = SFQ_DEPTH;
+ q->cur_depth = 0;
+ q->tail = NULL;
if (opt == NULL) {
q->quantum = psched_mtu(qdisc_dev(sch));
q->perturb_period = 0;
@@ -467,7 +532,7 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
return err;
}

- for (i = 0; i < SFQ_DEPTH; i++)
+ for (i = 0; i < SFQ_SLOTS; i++)
sfq_link(q, i);
return 0;
}
@@ -543,13 +608,12 @@ static int sfq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
struct gnet_dump *d)
{
struct sfq_sched_data *q = qdisc_priv(sch);
- sfq_index idx = q->ht[cl-1];
- struct sk_buff_head *list = &q->qs[idx];
- struct gnet_stats_queue qs = { .qlen = list->qlen };
- struct tc_sfq_xstats xstats = { .allot = q->allot[idx] };
+ const struct sfq_slot *slot = &q->slots[q->ht[cl - 1]];
+ struct gnet_stats_queue qs = { .qlen = slot->qlen };
+ struct tc_sfq_xstats xstats = { .allot = slot->allot };
struct sk_buff *skb;

- skb_queue_walk(list, skb)
+ slot_queue_walk(slot, skb)
qs.backlog += qdisc_pkt_len(skb);

if (gnet_stats_copy_queue(d, &qs) < 0)
@@ -566,7 +630,7 @@ static void sfq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
return;

for (i = 0; i < SFQ_HASH_DIVISOR; i++) {
- if (q->ht[i] == SFQ_DEPTH ||
+ if (q->ht[i] == SFQ_EMPTY_SLOT ||
arg->count < arg->skip) {
arg->count++;
continue;