mac80211: Tx frame latency statistics

Measure TX latency and jitter statistics per station per TID.
These Measurements are disabled by default and can be enabled
via debugfs.

Features included for each station's TID:

1. Keep count of the maximum and average latency of Tx frames.
2. Keep track of many frames arrived in a specific time range
   (need to enable through debugfs and configure the bins ranges)

Signed-off-by: Matti Gottlieb <matti.gottlieb@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 78 insertions, 0 deletions

diff --git a/net/mac80211/status.c b/net/mac80211/status.c
index 52a152b01b06..1ee85c402439 100644
--- a/net/mac80211/status.c
+++ b/net/mac80211/status.c
@@ -11,6 +11,7 @@
 
 #include <linux/export.h>
 #include <linux/etherdevice.h>
+#include <linux/time.h>
 #include <net/mac80211.h>
 #include <asm/unaligned.h>
 #include "ieee80211_i.h"
@@ -463,6 +464,77 @@ static void ieee80211_report_used_skb(struct ieee80211_local *local,
 }
 
 /*
+ * Measure Tx frame completion and removal time for Tx latency statistics
+ * calculation. A single Tx frame latency should be measured from when it
+ * is entering the Kernel until we receive Tx complete confirmation indication
+ * and remove the skb.
+ */
+static void ieee80211_tx_latency_end_msrmnt(struct ieee80211_local *local,
+                                            struct sk_buff *skb,
+                                            struct sta_info *sta,
+                                            struct ieee80211_hdr *hdr)
+{
+        ktime_t skb_dprt;
+        struct timespec dprt_time;
+        u32 msrmnt;
+        u16 tid;
+        u8 *qc;
+        int i, bin_range_count, bin_count;
+        u32 *bin_ranges;
+        __le16 fc;
+        struct ieee80211_tx_latency_stat *tx_lat;
+        struct ieee80211_tx_latency_bin_ranges *tx_latency;
+        ktime_t skb_arv = skb->tstamp;
+
+        tx_latency = rcu_dereference(local->tx_latency);
+
+        /* assert Tx latency stats are enabled & frame arrived when enabled */
+        if (!tx_latency || !ktime_to_ns(skb_arv))
+                return;
+
+        fc = hdr->frame_control;
+
+        if (!ieee80211_is_data(fc)) /* make sure it is a data frame */
+                return;
+
+        /* get frame tid */
+        if (ieee80211_is_data_qos(hdr->frame_control)) {
+                qc = ieee80211_get_qos_ctl(hdr);
+                tid = qc[0] & IEEE80211_QOS_CTL_TID_MASK;
+        } else {
+                tid = 0;
+        }
+
+        tx_lat = &sta->tx_lat[tid];
+
+        ktime_get_ts(&dprt_time); /* time stamp completion time */
+        skb_dprt = ktime_set(dprt_time.tv_sec, dprt_time.tv_nsec);
+        msrmnt = ktime_to_ms(ktime_sub(skb_dprt, skb_arv));
+
+        if (tx_lat->max < msrmnt) /* update stats */
+                tx_lat->max = msrmnt;
+        tx_lat->counter++;
+        tx_lat->sum += msrmnt;
+
+        if (!tx_lat->bins) /* bins not activated */
+                return;
+
+        /* count how many Tx frames transmitted with the appropriate latency */
+        bin_range_count = tx_latency->n_ranges;
+        bin_ranges = tx_latency->ranges;
+        bin_count = tx_lat->bin_count;
+
+        for (i = 0; i < bin_range_count; i++) {
+                if (msrmnt <= bin_ranges[i]) {
+                        tx_lat->bins[i]++;
+                        break;
+                }
+        }
+        if (i == bin_range_count) /* msrmnt is bigger than the biggest range */
+                tx_lat->bins[i]++;
+}
+
+/*
  * Use a static threshold for now, best value to be determined
  * by testing ...
  * Should it depend on:
@@ -620,6 +692,12 @@ void ieee80211_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb)
 
                 if (acked)
                         sta->last_ack_signal = info->status.ack_signal;
+
+                /*
+                 * Measure frame removal for tx latency
+                 * statistics calculation
+                 */
+                ieee80211_tx_latency_end_msrmnt(local, skb, sta, hdr);
         }
 
         rcu_read_unlock();