net/fq_impl: do not maintain a backlog-sorted list of flows

A sorted flow list is only needed to drop packets in the biggest flow when
hitting the overmemory condition.
By scanning flows only when needed, we can avoid paying the cost of
maintaining the list under normal conditions
In order to avoid scanning lots of empty flows and touching too many cold
cache lines, a bitmap of flows with backlog is maintained

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20201218184718.93650-3-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 67 insertions, 46 deletions

diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h
index dd374c7f0fe5..a5f67a2c0c73 100644
--- a/include/net/fq_impl.h
+++ b/include/net/fq_impl.h
@@ -17,12 +17,24 @@ __fq_adjust_removal(struct fq *fq, struct fq_flow *flow, unsigned int packets,
 		    unsigned int bytes, unsigned int truesize)
 {
 	struct fq_tin *tin = flow->tin;
+	int idx;
 
 	tin->backlog_bytes -= bytes;
 	tin->backlog_packets -= packets;
 	flow->backlog -= bytes;
 	fq->backlog -= packets;
 	fq->memory_usage -= truesize;
+
+	if (flow->backlog)
+		return;
+
+	if (flow == &tin->default_flow) {
+		list_del_init(&tin->tin_list);
+		return;
+	}
+
+	idx = flow - fq->flows;
+	__clear_bit(idx, fq->flows_bitmap);
 }
 
 static void fq_adjust_removal(struct fq *fq,
@@ -32,24 +44,6 @@ static void fq_adjust_removal(struct fq *fq,
 	__fq_adjust_removal(fq, flow, 1, skb->len, skb->truesize);
 }
 
-static void fq_rejigger_backlog(struct fq *fq, struct fq_flow *flow)
-{
-	struct fq_flow *i;
-
-	if (flow->backlog == 0) {
-		list_del_init(&flow->backlogchain);
-	} else {
-		i = flow;
-
-		list_for_each_entry_continue(i, &fq->backlogs, backlogchain)
-			if (i->backlog < flow->backlog)
-				break;
-
-		list_move_tail(&flow->backlogchain,
-			       &i->backlogchain);
-	}
-}
-
 static struct sk_buff *fq_flow_dequeue(struct fq *fq,
 				       struct fq_flow *flow)
 {
@@ -62,7 +56,6 @@ static struct sk_buff *fq_flow_dequeue(struct fq *fq,
 		return NULL;
 
 	fq_adjust_removal(fq, flow, skb);
-	fq_rejigger_backlog(fq, flow);
 
 	return skb;
 }
@@ -90,7 +83,6 @@ static int fq_flow_drop(struct fq *fq, struct fq_flow *flow,
 	} while (packets < pending);
 
 	__fq_adjust_removal(fq, flow, packets, bytes, truesize);
-	fq_rejigger_backlog(fq, flow);
 
 	return packets;
 }
@@ -170,22 +162,36 @@ static struct fq_flow *fq_flow_classify(struct fq *fq,
 	return flow;
 }
 
-static void fq_recalc_backlog(struct fq *fq,
-			      struct fq_tin *tin,
-			      struct fq_flow *flow)
+static struct fq_flow *fq_find_fattest_flow(struct fq *fq)
 {
-	struct fq_flow *i;
+	struct fq_tin *tin;
+	struct fq_flow *flow = NULL;
+	u32 len = 0;
+	int i;
 
-	if (list_empty(&flow->backlogchain))
-		list_add_tail(&flow->backlogchain, &fq->backlogs);
+	for_each_set_bit(i, fq->flows_bitmap, fq->flows_cnt) {
+		struct fq_flow *cur = &fq->flows[i];
+		unsigned int cur_len;
 
-	i = flow;
-	list_for_each_entry_continue_reverse(i, &fq->backlogs,
-					     backlogchain)
-		if (i->backlog > flow->backlog)
-			break;
+		cur_len = cur->backlog;
+		if (cur_len <= len)
+			continue;
+
+		flow = cur;
+		len = cur_len;
+	}
+
+	list_for_each_entry(tin, &fq->tin_backlog, tin_list) {
+		unsigned int cur_len = tin->default_flow.backlog;
 
-	list_move(&flow->backlogchain, &i->backlogchain);
+		if (cur_len <= len)
+			continue;
+
+		flow = &tin->default_flow;
+		len = cur_len;
+	}
+
+	return flow;
 }
 
 static void fq_tin_enqueue(struct fq *fq,
@@ -200,6 +206,13 @@ static void fq_tin_enqueue(struct fq *fq,
 
 	flow = fq_flow_classify(fq, tin, idx, skb);
 
+	if (!flow->backlog) {
+		if (flow != &tin->default_flow)
+			__set_bit(idx, fq->flows_bitmap);
+		else if (list_empty(&tin->tin_list))
+			list_add(&tin->tin_list, &fq->tin_backlog);
+	}
+
 	flow->tin = tin;
 	flow->backlog += skb->len;
 	tin->backlog_bytes += skb->len;
@@ -207,8 +220,6 @@ static void fq_tin_enqueue(struct fq *fq,
 	fq->memory_usage += skb->truesize;
 	fq->backlog++;
 
-	fq_recalc_backlog(fq, tin, flow);
-
 	if (list_empty(&flow->flowchain)) {
 		flow->deficit = fq->quantum;
 		list_add_tail(&flow->flowchain,
@@ -218,9 +229,7 @@ static void fq_tin_enqueue(struct fq *fq,
 	__skb_queue_tail(&flow->queue, skb);
 	oom = (fq->memory_usage > fq->memory_limit);
 	while (fq->backlog > fq->limit || oom) {
-		flow = list_first_entry_or_null(&fq->backlogs,
-						struct fq_flow,
-						backlogchain);
+		flow = fq_find_fattest_flow(fq);
 		if (!flow)
 			return;
 
@@ -255,8 +264,6 @@ static void fq_flow_filter(struct fq *fq,
 		fq_adjust_removal(fq, flow, skb);
 		free_func(fq, tin, flow, skb);
 	}
-
-	fq_rejigger_backlog(fq, flow);
 }
 
 static void fq_tin_filter(struct fq *fq,
@@ -279,16 +286,18 @@ static void fq_flow_reset(struct fq *fq,
 			  struct fq_flow *flow,
 			  fq_skb_free_t free_func)
 {
+	struct fq_tin *tin = flow->tin;
 	struct sk_buff *skb;
 
 	while ((skb = fq_flow_dequeue(fq, flow)))
-		free_func(fq, flow->tin, flow, skb);
+		free_func(fq, tin, flow, skb);
 
-	if (!list_empty(&flow->flowchain))
+	if (!list_empty(&flow->flowchain)) {
 		list_del_init(&flow->flowchain);
-
-	if (!list_empty(&flow->backlogchain))
-		list_del_init(&flow->backlogchain);
+		if (list_empty(&tin->new_flows) &&
+		    list_empty(&tin->old_flows))
+			list_del_init(&tin->tin_list);
+	}
 
 	flow->tin = NULL;
 
@@ -314,6 +323,7 @@ static void fq_tin_reset(struct fq *fq,
 		fq_flow_reset(fq, flow, free_func);
 	}
 
+	WARN_ON_ONCE(!list_empty(&tin->tin_list));
 	WARN_ON_ONCE(tin->backlog_bytes);
 	WARN_ON_ONCE(tin->backlog_packets);
 }
@@ -321,7 +331,6 @@ static void fq_tin_reset(struct fq *fq,
 static void fq_flow_init(struct fq_flow *flow)
 {
 	INIT_LIST_HEAD(&flow->flowchain);
-	INIT_LIST_HEAD(&flow->backlogchain);
 	__skb_queue_head_init(&flow->queue);
 }
 
@@ -329,6 +338,7 @@ static void fq_tin_init(struct fq_tin *tin)
 {
 	INIT_LIST_HEAD(&tin->new_flows);
 	INIT_LIST_HEAD(&tin->old_flows);
+	INIT_LIST_HEAD(&tin->tin_list);
 	fq_flow_init(&tin->default_flow);
 }
 
@@ -337,8 +347,8 @@ static int fq_init(struct fq *fq, int flows_cnt)
 	int i;
 
 	memset(fq, 0, sizeof(fq[0]));
-	INIT_LIST_HEAD(&fq->backlogs);
 	spin_lock_init(&fq->lock);
+	INIT_LIST_HEAD(&fq->tin_backlog);
 	fq->flows_cnt = max_t(u32, flows_cnt, 1);
 	fq->quantum = 300;
 	fq->limit = 8192;
@@ -348,6 +358,14 @@ static int fq_init(struct fq *fq, int flows_cnt)
 	if (!fq->flows)
 		return -ENOMEM;
 
+	fq->flows_bitmap = kcalloc(BITS_TO_LONGS(fq->flows_cnt), sizeof(long),
+				   GFP_KERNEL);
+	if (!fq->flows_bitmap) {
+		kvfree(fq->flows);
+		fq->flows = NULL;
+		return -ENOMEM;
+	}
+
 	for (i = 0; i < fq->flows_cnt; i++)
 		fq_flow_init(&fq->flows[i]);
 
@@ -364,6 +382,9 @@ static void fq_reset(struct fq *fq,
 
 	kvfree(fq->flows);
 	fq->flows = NULL;
+
+	kfree(fq->flows_bitmap);
+	fq->flows_bitmap = NULL;
 }
 
 #endif