Re: [PATCH v2 net-next-2.6] sch_sfq: allow big packets and be fair

Jarek Poplawski
2010-12-21T13:47:12Z

On Tue, Dec 21, 2010 at 02:04:59PM +0100, Eric Dumazet wrote:
> Le mardi 21 décembre 2010 ?? 12:17 +0000, Jarek Poplawski a écrit :
>
> > Oops! You're right yet ;-) This skipping shouldn't happen with quantum
> > bigger than max packet size, so this patch is OK.
>
> Thanks Jarek, here is a v2 with the scale you suggested.

Very nice! Thanks as well,
Jarek P.

>
> [PATCH v2 net-next-2.6] sch_sfq: allow big packets and be fair
>
> SFQ is currently 'limited' to small packets, because it uses a 15bit
> allotment number per flow. Introduce a scale by 8, so that we can handle
> full size TSO/GRO packets.
>
> Use appropriate handling to make sure allot is positive before a new
> packet is dequeued, so that fairness is respected.
>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Jarek Poplawski <jarkao2@gmail.com>
> Cc: Patrick McHardy <kaber@trash.net>
> ---
> v2: Use a scale of 8 as Jarek suggested, instead of 18bit fields
>
> net/sched/sch_sfq.c | 28 +++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> index c474b4b..f3a9fd7 100644
> --- a/net/sched/sch_sfq.c
> +++ b/net/sched/sch_sfq.c
> @@ -67,7 +67,7 @@
>
> IMPLEMENTATION:
> This implementation limits maximal queue length to 128;
> - maximal mtu to 2^15-1; max 128 flows, number of hash buckets to 1024.
> + 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.
>
> @@ -77,6 +77,11 @@
> #define SFQ_SLOTS 128 /* max number of flows */
> #define SFQ_EMPTY_SLOT 255
> #define SFQ_HASH_DIVISOR 1024
> +/* We use 15+1 bits to store allot, and want to handle packets up to 64K
> + * Scale allot by 8 (1<<3) so that no overflow occurs.
> + */
> +#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;
> @@ -115,7 +120,7 @@ struct sfq_sched_data
> struct timer_list perturb_timer;
> u32 perturbation;
> 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[SFQ_HASH_DIVISOR]; /* Hash table */
> struct sfq_slot slots[SFQ_SLOTS];
> @@ -394,7 +399,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> q->tail->next = x;
> }
> q->tail = slot;
> - slot->allot = q->quantum;
> + slot->allot = q->scaled_quantum;
> }
> if (++sch->q.qlen <= q->limit) {
> sch->bstats.bytes += qdisc_pkt_len(skb);
> @@ -430,8 +435,14 @@ sfq_dequeue(struct Qdisc *sch)
> if (q->tail == NULL)
> return NULL;
>
> +next_slot:
> a = q->tail->next;
> slot = &q->slots[a];
> + if (slot->allot <= 0) {
> + q->tail = slot;
> + slot->allot += q->scaled_quantum;
> + goto next_slot;
> + }
> skb = slot_dequeue_head(slot);
> sfq_dec(q, a);
> sch->q.qlen--;
> @@ -446,9 +457,8 @@ sfq_dequeue(struct Qdisc *sch)
> return skb;
> }
> q->tail->next = next_a;
> - } else if ((slot->allot -= qdisc_pkt_len(skb)) <= 0) {
> - q->tail = slot;
> - slot->allot += q->quantum;
> + } else {
> + slot->allot -= SFQ_ALLOT_SIZE(qdisc_pkt_len(skb));
> }
> return skb;
> }
> @@ -484,6 +494,7 @@ static int sfq_change(struct Qdisc *sch, struct nlattr *opt)
>
> sch_tree_lock(sch);
> q->quantum = ctl->quantum ? : psched_mtu(qdisc_dev(sch));
> + 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);
> @@ -524,6 +535,7 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
> q->tail = NULL;
> if (opt == NULL) {
> q->quantum = psched_mtu(qdisc_dev(sch));
> + q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
> q->perturb_period = 0;
> q->perturbation = net_random();
> } else {
> @@ -610,7 +622,9 @@ static int sfq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
> struct sfq_sched_data *q = qdisc_priv(sch);
> 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 tc_sfq_xstats xstats = {
> + .allot = slot->allot << SFQ_ALLOT_SHIFT
> + };
> struct sk_buff *skb;
>
> slot_queue_walk(slot, skb)
>
>