[PATCH 3/5] mac80211: calculate hash for fq without holding fq->lock in itxq enqueue

[Felix Fietkau]

Reduces lock contention on enqueue/dequeue of iTXQ packets

Signed-off-by: Felix Fietkau <n...@nbd.name>
---
 include/net/fq_impl.h | 18 ++++++++++--------
 net/mac80211/tx.c     | 15 ++++++++++-----
 2 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h
index be7c0fab3478..2caa86660ab0 100644
--- a/include/net/fq_impl.h
+++ b/include/net/fq_impl.h
@@ -107,21 +107,23 @@ static struct sk_buff *fq_tin_dequeue(struct fq *fq,
        return skb;
 }
 
+static u32 fq_flow_idx(struct fq *fq, struct sk_buff *skb)
+{
+       u32 hash = skb_get_hash_perturb(skb, fq->perturbation);
+
+       return reciprocal_scale(hash, fq->flows_cnt);
+}
+
 static struct fq_flow *fq_flow_classify(struct fq *fq,
-                                       struct fq_tin *tin,
+                                       struct fq_tin *tin, u32 idx,
                                        struct sk_buff *skb,
                                        fq_flow_get_default_t get_default_func)
 {
        struct fq_flow *flow;
-       u32 hash;
-       u32 idx;
 
        lockdep_assert_held(&fq->lock);
 
-       hash = skb_get_hash_perturb(skb, fq->perturbation);
-       idx = reciprocal_scale(hash, fq->flows_cnt);
        flow = &fq->flows[idx];
-
        if (flow->tin && flow->tin != tin) {
                flow = get_default_func(fq, tin, idx, skb);
                tin->collisions++;
@@ -153,7 +155,7 @@ static void fq_recalc_backlog(struct fq *fq,
 }
 
 static void fq_tin_enqueue(struct fq *fq,
-                          struct fq_tin *tin,
+                          struct fq_tin *tin, u32 idx,
                           struct sk_buff *skb,
                           fq_skb_free_t free_func,
                           fq_flow_get_default_t get_default_func)
@@ -163,7 +165,7 @@ static void fq_tin_enqueue(struct fq *fq,
 
        lockdep_assert_held(&fq->lock);
 
-       flow = fq_flow_classify(fq, tin, skb, get_default_func);
+       flow = fq_flow_classify(fq, tin, idx, skb, get_default_func);
 
        flow->tin = tin;
        flow->backlog += skb->len;
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 0b73a0fe8218..8127e43e12b1 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1398,11 +1398,15 @@ static void ieee80211_txq_enqueue(struct 
ieee80211_local *local,
 {
        struct fq *fq = &local->fq;
        struct fq_tin *tin = &txqi->tin;
+       u32 flow_idx = fq_flow_idx(fq, skb);
 
        ieee80211_set_skb_enqueue_time(skb);
-       fq_tin_enqueue(fq, tin, skb,
+
+       spin_lock_bh(&fq->lock);
+       fq_tin_enqueue(fq, tin, flow_idx, skb,
                       fq_skb_free_func,
                       fq_flow_get_default_func);
+       spin_unlock_bh(&fq->lock);
 }
 
 static bool fq_vlan_filter_func(struct fq *fq, struct fq_tin *tin,
@@ -1589,7 +1593,6 @@ static bool ieee80211_queue_skb(struct ieee80211_local 
*local,
                                struct sta_info *sta,
                                struct sk_buff *skb)
 {
-       struct fq *fq = &local->fq;
        struct ieee80211_vif *vif;
        struct txq_info *txqi;
 
@@ -1607,9 +1610,7 @@ static bool ieee80211_queue_skb(struct ieee80211_local 
*local,
        if (!txqi)
                return false;
 
-       spin_lock_bh(&fq->lock);
        ieee80211_txq_enqueue(local, txqi, skb);
-       spin_unlock_bh(&fq->lock);
 
        schedule_and_wake_txq(local, txqi);
 
@@ -3227,6 +3228,7 @@ static bool ieee80211_amsdu_aggregate(struct 
ieee80211_sub_if_data *sdata,
        u8 max_subframes = sta->sta.max_amsdu_subframes;
        int max_frags = local->hw.max_tx_fragments;
        int max_amsdu_len = sta->sta.max_amsdu_len;
+       u32 flow_idx;
        int orig_truesize;
        __be16 len;
        void *data;
@@ -3256,6 +3258,8 @@ static bool ieee80211_amsdu_aggregate(struct 
ieee80211_sub_if_data *sdata,
                max_amsdu_len = min_t(int, max_amsdu_len,
                                      sta->sta.max_tid_amsdu_len[tid]);
 
+       flow_idx = fq_flow_idx(fq, skb);
+
        spin_lock_bh(&fq->lock);
 
        /* TODO: Ideally aggregation should be done on dequeue to remain
@@ -3263,7 +3267,8 @@ static bool ieee80211_amsdu_aggregate(struct 
ieee80211_sub_if_data *sdata,
         */
 
        tin = &txqi->tin;
-       flow = fq_flow_classify(fq, tin, skb, fq_flow_get_default_func);
+       flow = fq_flow_classify(fq, tin, flow_idx, skb,
+                               fq_flow_get_default_func);
        head = skb_peek_tail(&flow->queue);
        if (!head || skb_is_gso(head))
                goto out;
-- 
2.17.0