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   1 From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
   2 Date: Wed, 23 Oct 2019 11:59:00 +0200
   3 Subject: [PATCH] mac80211: Shrink the size of ack_frame_id to make room for
   4  tx_time_est
   5 MIME-Version: 1.0
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   8
   9 To implement airtime queue limiting, we need to keep a running account of
  10 the estimated airtime of all skbs queued into the device. Do to this
  11 correctly, we need to store the airtime estimate into the skb so we can
  12 decrease the outstanding balance when the skb is freed. This means that the
  13 time estimate must be stored somewhere that will survive for the lifetime
  14 of the skb.
  15
  16 To get this, decrease the size of the ack_frame_id field to 6 bits, and
  17 lower the size of the ID space accordingly. This leaves 10 bits for use for
  18 tx_time_est, which is enough to store a maximum of 4096 us, if we shift the
  19 values so they become units of 4us.
  20
  21 Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
  22 Link: https://lore.kernel.org/r/157182474063.150713.16132669599100802716.stgit@toke.dk
  23 Signed-off-by: Johannes Berg <johannes.berg@intel.com>
  24 ---
  25
  26 --- a/include/net/mac80211.h
  27 +++ b/include/net/mac80211.h
  28 @@ -967,6 +967,7 @@ ieee80211_rate_get_vht_nss(const struct
  29   * @band: the band to transmit on (use for checking for races)
  30   * @hw_queue: HW queue to put the frame on, skb_get_queue_mapping() gives the AC
  31   * @ack_frame_id: internal frame ID for TX status, used internally
  32 + * @tx_time_est: TX time estimate in units of 4us, used internally
  33   * @control: union part for control data
  34   * @control.rates: TX rates array to try
  35   * @control.rts_cts_rate_idx: rate for RTS or CTS
  36 @@ -1007,7 +1008,8 @@ struct ieee80211_tx_info {
  37
  38         u8 hw_queue;
  39
  40 -       u16 ack_frame_id;
  41 +       u16 ack_frame_id:6;
  42 +       u16 tx_time_est:10;
  43
  44         union {
  45                 struct {
  46 --- a/net/mac80211/cfg.c
  47 +++ b/net/mac80211/cfg.c
  48 @@ -3427,7 +3427,7 @@ int ieee80211_attach_ack_skb(struct ieee
  49
  50         spin_lock_irqsave(&local->ack_status_lock, spin_flags);
  51         id = idr_alloc(&local->ack_status_frames, ack_skb,
  52 -                      1, 0x10000, GFP_ATOMIC);
  53 +                      1, 0x40, GFP_ATOMIC);
  54         spin_unlock_irqrestore(&local->ack_status_lock, spin_flags);
  55
  56         if (id < 0) {
  57 --- a/net/mac80211/tx.c
  58 +++ b/net/mac80211/tx.c
  59 @@ -2443,7 +2443,7 @@ static int ieee80211_store_ack_skb(struc
  60
  61                 spin_lock_irqsave(&local->ack_status_lock, flags);
  62                 id = idr_alloc(&local->ack_status_frames, ack_skb,
  63 -                              1, 0x10000, GFP_ATOMIC);
  64 +                              1, 0x40, GFP_ATOMIC);
  65                 spin_unlock_irqrestore(&local->ack_status_lock, flags);
  66
  67                 if (id >= 0) {