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Date: Wed, 11 Dec 2013 12:37:10 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: Terry Lam <vtlam@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>,
Nandita Dukkipati <nanditad@...gle.com>
Subject: Re: [PATCH] net-qdisc-hhf: Heavy-Hitter Filter (HHF) qdisc
On Tue, 10 Dec 2013 23:26:36 -0800
Terry Lam <vtlam@...gle.com> wrote:
> This patch implements the first size-based qdisc that attempts to
> differentiate between small flows and heavy-hitters. The goal is to
> catch the heavy-hitters and move them to a separate queue with less
> priority so that bulk traffic does not affect the latency of critical
> traffic. Currently "less priority" means less weight (2:1 in
> particular) in a Weighted Deficit Round Robin (WDRR) scheduler.
>
> In essence, this patch addresses the "delay-bloat" problem due to
> bloated buffers. In some systems, large queues may be necessary for
> obtaining CPU efficiency, or due to the presence of unresponsive
> traffic like UDP, or just a large number of connections with each
> having a small amount of outstanding traffic. In these circumstances,
> HHF aims to reduce the HoL blocking for latency sensitive traffic,
> while not impacting the queues built up by bulk traffic. HHF can also
> be used in conjunction with other AQM mechanisms such as CoDel.
>
> To capture heavy-hitters, we implement the "multi-stage filter" design
> in the following paper:
> C. Estan and G. Varghese, "New Directions in Traffic Measurement and
> Accounting", in ACM SIGCOMM, 2002.
>
> Some configurable qdisc settings through 'tc':
> - hhf_reset_timeout: period to reset counter values in the multi-stage
> filter (default 40ms)
> - hhf_admit_bytes: threshold to classify heavy-hitters
> (default 128KB)
> - hhf_evict_timeout: threshold to evict idle heavy-hitters
> (default 1s)
> - hhf_non_hh_weight: Weighted Deficit Round Robin (WDRR) weight for
> non-heavy-hitters (default 2)
> - hh_flows_limit: max number of heavy-hitter flow entries
> (default 2048)
>
> Note that the ratio between hhf_admit_bytes and hhf_reset_timeout
> reflects the bandwidth of heavy-hitters that we attempt to capture
> (25Mbps with the above default settings).
>
> The false negative rate (heavy-hitter flows getting away unclassified)
> is zero by the design of the multi-stage filter algorithm.
> With 100 heavy-hitter flows, using four hashes and 4000 counters yields
> a false positive rate (non-heavy-hitters mistakenly classified as
> heavy-hitters) of less than 1e-4.
>
> Signed-off-by: Terry Lam <vtlam@...gle.com>
> ---
> include/uapi/linux/pkt_sched.h | 25 ++
> net/sched/Kconfig | 9 +
> net/sched/Makefile | 1 +
> net/sched/sch_hhf.c | 746 +++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 781 insertions(+)
> create mode 100644 net/sched/sch_hhf.c
>
> diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
> index a806687..4566993 100644
> --- a/include/uapi/linux/pkt_sched.h
> +++ b/include/uapi/linux/pkt_sched.h
> @@ -790,4 +790,29 @@ struct tc_fq_qd_stats {
> __u32 throttled_flows;
> __u32 pad;
> };
> +
> +/* Heavy-Hitter Filter */
> +
> +enum {
> + TCA_HHF_UNSPEC,
> + TCA_HHF_BACKLOG_LIMIT,
> + TCA_HHF_QUANTUM,
> + TCA_HHF_HH_FLOWS_LIMIT,
> + TCA_HHF_RESET_TIMEOUT,
> + TCA_HHF_ADMIT_BYTES,
> + TCA_HHF_EVICT_TIMEOUT,
> + TCA_HHF_NON_HH_WEIGHT,
> + __TCA_HHF_MAX
> +};
> +
> +#define TCA_HHF_MAX (__TCA_HHF_MAX - 1)
> +
> +struct tc_hhf_xstats {
> + __u32 drop_overlimit; /* number of times max qdisc packet limit
> + * was hit
> + */
64 bit?
> + __u32 hh_overlimit; /* number of times max heavy-hitters was hit */
> + __u32 hh_tot_count; /* number of captured heavy-hitters so far */
> + __u32 hh_cur_count; /* number of current heavy-hitters */
> +};
> #endif
> diff --git a/net/sched/sch_hhf.c b/net/sched/sch_hhf.c
> new file mode 100644
> index 0000000..91c723e
> --- /dev/null
> +++ b/net/sched/sch_hhf.c
> @@ -0,0 +1,746 @@
> +#define hhf_time_before(a, b) \
> + (typecheck(u32, a) && typecheck(u32, b) && ((s32)((a) - (b)) < 0))
Why reinvent time_before?
> +
> +/* Heavy-hitter per-flow state */
> +struct hh_flow_state {
> + u32 hash_id; /* hash of flow-id (e.g. TCP 5-tuple) */
> + u32 hit_timestamp; /* last time heavy-hitter was seen */
> + struct list_head flowchain; /* chaining under hash collision */
> +};
> +
> +/* Weighted Deficit Round Robin (WDRR) scheduler */
> +struct wdrr_bucket {
> + struct sk_buff *head;
> + struct sk_buff *tail;
> + struct list_head bucketchain;
> + int deficit;
> +};
> +
> +struct hhf_sched_data {
> + struct wdrr_bucket buckets[WDRR_BUCKET_CNT];
> + u32 perturbation; /* hash perturbation */
> + u32 quantum; /* psched_mtu(qdisc_dev(sch)); */
> + u32 drop_overlimit; /* number of times max qdisc packet
> + * limit was hit
> + */
> + struct list_head *hh_flows; /* table T (currently active HHs) */
> + u32 hh_flows_limit; /* max active HH allocs */
> + u32 hh_flows_overlimit; /* num of disallowed HH allocs */
> + u32 hh_flows_total_cnt; /* total admitted HHs */
> + u32 hh_flows_current_cnt; /* total current HHs */
> + u32 *hhf_arrays[HHF_ARRAYS_CNT]; /* HH filter F */
> + u32 hhf_arrays_reset_timestamp; /* last time hhf_arrays
> + * was reset
> + */
> + unsigned long *hhf_valid_bits[HHF_ARRAYS_CNT]; /* shadow valid bits
> + * of hhf_arrays
> + */
> + /* Similar to the "new_flows" vs. "old_flows" concept in fq_codel DRR */
> + struct list_head new_buckets; /* list of new buckets */
> + struct list_head old_buckets; /* list of old buckets */
> +
> + /* Configurable HHF parameters */
> + u32 hhf_reset_timeout; /* interval to reset counter
> + * arrays in filter F
> + * (default 40ms)
> + */
> + u32 hhf_admit_bytes; /* counter thresh to classify as
> + * HH (default 128KB).
> + * With these default values,
> + * 128KB / 40ms = 25 Mbps
> + * i.e., we expect to capture HHs
> + * sending > 25 Mbps.
> + */
> + u32 hhf_evict_timeout; /* aging threshold to evict idle
> + * HHs out of table T. This should
> + * be large enough to avoid
> + * reordering during HH eviction.
> + * (default 1s)
> + */
> + u32 hhf_non_hh_weight; /* WDRR weight for non-HHs
> + * (default 2,
> + * i.e., non-HH : HH = 2 : 1)
> + */
> +};
> +
> +static inline u32 hhf_time_stamp(void)
> +{
> + return jiffies;
> +}
Why wrap jiffies needlessly
> +static unsigned int skb_hash(const struct hhf_sched_data *q,
> + const struct sk_buff *skb)
> +{
> + struct flow_keys keys;
> + unsigned int hash;
> +
> + if (skb->sk && skb->sk->sk_hash)
> + return skb->sk->sk_hash;
> +
> + skb_flow_dissect(skb, &keys);
> + hash = jhash_3words((__force u32)keys.dst,
> + (__force u32)keys.src ^ keys.ip_proto,
> + (__force u32)keys.ports, q->perturbation);
> + return hash;
> +}
Why not reuse flow dissect logic that exists in SFQ?
> +/* Looks up a heavy-hitter flow in a chaining list of table T. */
> +static inline struct hh_flow_state *seek_list(const u32 hash,
> + struct list_head *head,
> + struct hhf_sched_data *q)
Don't use inline. Let compiler decide.
> +{
> + struct hh_flow_state *flow, *next;
> + u32 now = hhf_time_stamp();
> +
> + if (list_empty(head))
> + return NULL;
> +
> + list_for_each_entry_safe(flow, next, head, flowchain) {
> + u32 prev = flow->hit_timestamp + q->hhf_evict_timeout;
> +
> + if (hhf_time_before(prev, now)) {
> + /* Delete expired heavy-hitters, but preserve one entry
> + * to avoid kzalloc() when next time this slot is hit.
> + */
> + if (list_is_last(&flow->flowchain, head))
> + return NULL;
> + list_del(&flow->flowchain);
> + kfree(flow);
> + q->hh_flows_current_cnt--;
> + } else if (flow->hash_id == hash) {
> + return flow;
> + }
> + }
> + return NULL;
> +}
> +
> +/* Returns a flow state entry for a new heavy-hitter. Either reuses an expired
> + * entry or dynamically alloc a new entry.
> + */
> +static inline struct hh_flow_state *alloc_new_hh(struct list_head *head,
> + struct hhf_sched_data *q)
> +{
> + struct hh_flow_state *flow;
> + u32 now = hhf_time_stamp();
> +
> + if (!list_empty(head)) {
> + /* Find an expired heavy-hitter flow entry. */
> + list_for_each_entry(flow, head, flowchain) {
> + u32 prev = flow->hit_timestamp + q->hhf_evict_timeout;
> +
> + if (hhf_time_before(prev, now))
> + return flow;
> + }
> + }
> +
> + if (q->hh_flows_current_cnt >= q->hh_flows_limit) {
> + q->hh_flows_overlimit++;
> + return NULL;
> + }
> + /* Create new entry. */
> + flow = kzalloc(sizeof(struct hh_flow_state), GFP_ATOMIC);
> + if (!flow)
> + return NULL;
> +
> + q->hh_flows_current_cnt++;
> + INIT_LIST_HEAD(&flow->flowchain);
> + list_add_tail(&flow->flowchain, head);
> +
> + return flow;
> +}
> +
> +/* Assigns packets to WDRR buckets. Implements a multi-stage filter to
> + * classify heavy-hitters.
> + */
> +static enum wdrr_bucket_idx hhf_classify(struct sk_buff *skb, struct Qdisc *sch)
> +{
> + struct hhf_sched_data *q = qdisc_priv(sch);
> + u32 tmp_hash, hash;
> + u32 xorsum, filter_pos[HHF_ARRAYS_CNT], flow_pos;
> + struct hh_flow_state *flow;
> + u32 pkt_len, min_hhf_val;
> + int i;
> + u32 prev;
> + u32 now = hhf_time_stamp();
> +
> + /* Reset the HHF counter arrays if this is the right time. */
> + prev = q->hhf_arrays_reset_timestamp + q->hhf_reset_timeout;
> + if (hhf_time_before(prev, now)) {
> + for (i = 0; i < HHF_ARRAYS_CNT; i++)
> + bitmap_zero(q->hhf_valid_bits[i], HHF_ARRAYS_LEN);
> + q->hhf_arrays_reset_timestamp = now;
> + }
> +
> + /* Get hashed flow-id of the skb. */
> + hash = skb_hash(q, skb);
> +
> + /* Check if this packet belongs to an already established HH flow. */
> + flow_pos = hash & HHF_BIT_MASK;
> + flow = seek_list(hash, &q->hh_flows[flow_pos], q);
> + if (flow) { /* found its HH flow */
> + flow->hit_timestamp = now;
> + return WDRR_BUCKET_FOR_HH;
> + }
> +
> + /* Now pass the packet through the multi-stage filter. */
> + tmp_hash = hash;
> + xorsum = 0;
> + for (i = 0; i < HHF_ARRAYS_CNT - 1; i++) {
> + /* Split the skb_hash into three 10-bit chunks. */
> + filter_pos[i] = tmp_hash & HHF_BIT_MASK;
> + xorsum ^= filter_pos[i];
> + tmp_hash >>= HHF_BIT_MASK_LEN;
> + }
> + /* The last chunk is computed as XOR sum of other chunks. */
> + filter_pos[HHF_ARRAYS_CNT - 1] = xorsum ^ tmp_hash;
> +
> + pkt_len = qdisc_pkt_len(skb);
> + min_hhf_val = ~0U;
> + for (i = 0; i < HHF_ARRAYS_CNT; i++) {
> + u32 val;
> +
> + if (!test_bit(filter_pos[i], q->hhf_valid_bits[i])) {
> + q->hhf_arrays[i][filter_pos[i]] = 0;
> + __set_bit(filter_pos[i], q->hhf_valid_bits[i]);
> + }
> +
> + val = q->hhf_arrays[i][filter_pos[i]] + pkt_len;
> + if (min_hhf_val > val)
> + min_hhf_val = val;
> + }
> +
> + /* Found a new HH iff all counter values > HH admit threshold. */
> + if (min_hhf_val > q->hhf_admit_bytes) {
> + /* Just captured a new heavy-hitter. */
> + flow = alloc_new_hh(&q->hh_flows[flow_pos], q);
> + if (!flow) /* memory alloc problem */
> + return WDRR_BUCKET_FOR_NON_HH;
> + flow->hash_id = hash;
> + flow->hit_timestamp = now;
> + q->hh_flows_total_cnt++;
> +
> + /* By returning without updating counters in q->hhf_arrays,
> + * we implicitly implement "shielding" (see Optimization O1).
> + */
> + return WDRR_BUCKET_FOR_HH;
> + }
> +
> + /* Conservative update of HHF arrays (see Optimization O2). */
> + for (i = 0; i < HHF_ARRAYS_CNT; i++) {
> + if (q->hhf_arrays[i][filter_pos[i]] < min_hhf_val)
> + q->hhf_arrays[i][filter_pos[i]] = min_hhf_val;
> + }
> + return WDRR_BUCKET_FOR_NON_HH;
> +}
> +
> +/* Removes one skb from head of bucket. */
> +static inline struct sk_buff *dequeue_head(struct wdrr_bucket *bucket)
> +{
> + struct sk_buff *skb = bucket->head;
> +
> + bucket->head = skb->next;
> + skb->next = NULL;
> + return skb;
> +}
Seems like reinvention of sk_list??
> +
> +/* Tail-adds skb to bucket. */
> +static inline void bucket_add(struct wdrr_bucket *bucket, struct sk_buff *skb)
> +{
> + if (bucket->head == NULL)
> + bucket->head = skb;
> + else
> + bucket->tail->next = skb;
> + bucket->tail = skb;
> + skb->next = NULL;
> +}
> +
> +static unsigned int hhf_drop(struct Qdisc *sch)
> +{
> + struct hhf_sched_data *q = qdisc_priv(sch);
> + struct wdrr_bucket *bucket;
> +
> + /* Always try to drop from heavy-hitters first. */
> + bucket = &q->buckets[WDRR_BUCKET_FOR_HH];
> + if (!bucket->head)
> + bucket = &q->buckets[WDRR_BUCKET_FOR_NON_HH];
> +
> + if (bucket->head) {
> + struct sk_buff *skb = dequeue_head(bucket);
> +
> + sch->q.qlen--;
> + sch->qstats.drops++;
> + sch->qstats.backlog -= qdisc_pkt_len(skb);
> + kfree_skb(skb);
> + }
> +
> + /* Return id of the bucket from which the packet was dropped. */
> + return bucket - q->buckets;
> +}
> +
> +static int hhf_enqueue(struct sk_buff *skb, struct Qdisc *sch)
> +{
> + struct hhf_sched_data *q = qdisc_priv(sch);
> + enum wdrr_bucket_idx idx;
> + struct wdrr_bucket *bucket;
> +
> + idx = hhf_classify(skb, sch);
> +
> + bucket = &q->buckets[idx];
> + bucket_add(bucket, skb);
> + sch->qstats.backlog += qdisc_pkt_len(skb);
> +
> + if (list_empty(&bucket->bucketchain)) {
> + unsigned int weight;
> +
> + /* The logic of new_buckets vs. old_buckets is the same as
> + * new_flows vs. old_flows in the implementation of fq_codel,
> + * i.e., short bursts of non-HHs should have strict priority.
> + */
> + if (idx == WDRR_BUCKET_FOR_HH) {
> + /* Always move heavy-hitters to old bucket. */
> + weight = 1;
> + list_add_tail(&bucket->bucketchain, &q->old_buckets);
> + } else {
> + weight = q->hhf_non_hh_weight;
> + list_add_tail(&bucket->bucketchain, &q->new_buckets);
> + }
> + bucket->deficit = weight * q->quantum;
> + }
> + if (++sch->q.qlen < sch->limit)
> + return NET_XMIT_SUCCESS;
> +
> + q->drop_overlimit++;
> + /* Return Congestion Notification only if we dropped a packet from this
> + * bucket.
> + */
> + if (hhf_drop(sch) == idx)
> + return NET_XMIT_CN;
> +
> + /* As we dropped a packet, better let upper stack know this. */
> + qdisc_tree_decrease_qlen(sch, 1);
> + return NET_XMIT_SUCCESS;
> +}
> +
> +static struct sk_buff *hhf_dequeue(struct Qdisc *sch)
> +{
> + struct hhf_sched_data *q = qdisc_priv(sch);
> + struct sk_buff *skb = NULL;
> + struct wdrr_bucket *bucket;
> + struct list_head *head;
> +
> +begin:
> + head = &q->new_buckets;
> + if (list_empty(head)) {
> + head = &q->old_buckets;
> + if (list_empty(head))
> + return NULL;
> + }
> + bucket = list_first_entry(head, struct wdrr_bucket, bucketchain);
> +
> + if (bucket->deficit <= 0) {
> + int weight = (bucket - q->buckets == WDRR_BUCKET_FOR_HH) ?
> + 1 : q->hhf_non_hh_weight;
> +
> + bucket->deficit += weight * q->quantum;
> + list_move_tail(&bucket->bucketchain, &q->old_buckets);
> + goto begin;
> + }
> +
> + if (bucket->head) {
> + skb = dequeue_head(bucket);
> + sch->q.qlen--;
> + sch->qstats.backlog -= qdisc_pkt_len(skb);
> + }
> +
> + if (!skb) {
> + /* Force a pass through old_buckets to prevent starvation. */
> + if ((head == &q->new_buckets) && !list_empty(&q->old_buckets))
> + list_move_tail(&bucket->bucketchain, &q->old_buckets);
> + else
> + list_del_init(&bucket->bucketchain);
> + goto begin;
> + }
> + qdisc_bstats_update(sch, skb);
> + bucket->deficit -= qdisc_pkt_len(skb);
> +
> + return skb;
> +}
> +
> +static void hhf_reset(struct Qdisc *sch)
> +{
> + struct sk_buff *skb;
> +
> + while ((skb = hhf_dequeue(sch)) != NULL)
> + kfree_skb(skb);
> +}
> +
> +static void *hhf_zalloc(size_t sz)
> +{
> + void *ptr = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN);
> +
> + if (!ptr)
> + ptr = vzalloc(sz);
> +
> + return ptr;
> +}
Are you really allocating thing so big that kmalloc fails?
If so, please base it on size > PAGE_SIZE
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