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Date: Wed, 11 Dec 2013 15:50:43 -0800
From: Tom Herbert <therbert@...gle.com>
To: Stephen Hemminger <stephen@...workplumber.org>
Cc: Terry Lam <vtlam@...gle.com>,
"David S. Miller" <davem@...emloft.net>,
Linux Netdev List <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 Wed, Dec 11, 2013 at 12:37 PM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> 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?
>
This could be a library function to to get the "txhash" for an skb,
most of it should also be in a common function with __skb_get_rxhash.
Does not applying the perturbation in the case of a hash in the socket
cause a loss of functionality?
>
>> +/* 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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