On Mon, Feb 8, 2016 at 10:38 AM, Felix Fietkau <nbd@xxxxxxxxxxx> wrote:
> Requires software tx queueing support. frag_list support (for zero-copy)
> is optional.
>
> Signed-off-by: Felix Fietkau <nbd@xxxxxxxxxxx>
> ---
Ok - looks fine, but... and here comes the hard stuff.
The frame size in the PLCP is limited in a way that you can't - from a
spec POV - enable A-MSDU for low rates. Of course, you don't want to
do that for low rates at all regardless of the spec.
Since you build the A-MSDU in the mac80211 Tx queue which is not aware
of the link quality, how do we prevent A-MSDU if the rate is low /
dropping.
I'd even argue that when the rates get lower, you'll have more
packets piling up in the software queue and ... even more chance to
get A-MSDU in the exact case where you really want to avoid it?
> include/net/mac80211.h | 13 ++++
> net/mac80211/agg-tx.c | 5 ++
> net/mac80211/debugfs.c | 2 +
> net/mac80211/ieee80211_i.h | 1 +
> net/mac80211/tx.c | 160 +++++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 181 insertions(+)
>
> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
> index 5714774..8c28210 100644
> --- a/include/net/mac80211.h
> +++ b/include/net/mac80211.h
> @@ -709,6 +709,7 @@ enum mac80211_tx_info_flags {
> * @IEEE80211_TX_CTRL_PS_RESPONSE: This frame is a response to a poll
> * frame (PS-Poll or uAPSD).
> * @IEEE80211_TX_CTRL_RATE_INJECT: This frame is injected with rate information
> + * @IEEE80211_TX_CTRL_AMSDU: This frame is an A-MSDU frame
> *
> * These flags are used in tx_info->control.flags.
> */
> @@ -716,6 +717,7 @@ enum mac80211_tx_control_flags {
> IEEE80211_TX_CTRL_PORT_CTRL_PROTO = BIT(0),
> IEEE80211_TX_CTRL_PS_RESPONSE = BIT(1),
> IEEE80211_TX_CTRL_RATE_INJECT = BIT(2),
> + IEEE80211_TX_CTRL_AMSDU = BIT(3),
> };
>
> /*
> @@ -1964,6 +1966,12 @@ struct ieee80211_txq {
> * order and does not need to manage its own reorder buffer or BA session
> * timeout.
> *
> + * @IEEE80211_HW_TX_AMSDU: Hardware (or driver) supports software aggregated
> + * A-MSDU frames. Requires software tx queueing support.
> + *
> + * @IEEE80211_HW_TX_FRAG_LIST: Hardware (or driver) supports sending frag_list
> + * skbs, needed for zero-copy software A-MSDU.
> + *
> * @NUM_IEEE80211_HW_FLAGS: number of hardware flags, used for sizing arrays
> */
> enum ieee80211_hw_flags {
> @@ -2001,6 +2009,8 @@ enum ieee80211_hw_flags {
> IEEE80211_HW_BEACON_TX_STATUS,
> IEEE80211_HW_NEEDS_UNIQUE_STA_ADDR,
> IEEE80211_HW_SUPPORTS_REORDERING_BUFFER,
> + IEEE80211_HW_TX_AMSDU,
> + IEEE80211_HW_TX_FRAG_LIST,
>
> /* keep last, obviously */
> NUM_IEEE80211_HW_FLAGS
> @@ -2073,6 +2083,8 @@ enum ieee80211_hw_flags {
> * size is smaller (an example is LinkSys WRT120N with FW v1.0.07
> * build 002 Jun 18 2012).
> *
> + * @max_tx_fragments: maximum fragments per (A-)MSDU.
> + *
> * @offchannel_tx_hw_queue: HW queue ID to use for offchannel TX
> * (if %IEEE80211_HW_QUEUE_CONTROL is set)
> *
> @@ -2127,6 +2139,7 @@ struct ieee80211_hw {
> u8 max_rate_tries;
> u8 max_rx_aggregation_subframes;
> u8 max_tx_aggregation_subframes;
> + u8 max_tx_fragments;
> u8 offchannel_tx_hw_queue;
> u8 radiotap_mcs_details;
> u16 radiotap_vht_details;
> diff --git a/net/mac80211/agg-tx.c b/net/mac80211/agg-tx.c
> index 4932e9f..42fa810 100644
> --- a/net/mac80211/agg-tx.c
> +++ b/net/mac80211/agg-tx.c
> @@ -935,6 +935,7 @@ void ieee80211_process_addba_resp(struct ieee80211_local *local,
> size_t len)
> {
> struct tid_ampdu_tx *tid_tx;
> + struct ieee80211_txq *txq;
> u16 capab, tid;
> u8 buf_size;
> bool amsdu;
> @@ -945,6 +946,10 @@ void ieee80211_process_addba_resp(struct ieee80211_local *local,
> buf_size = (capab & IEEE80211_ADDBA_PARAM_BUF_SIZE_MASK) >> 6;
> buf_size = min(buf_size, local->hw.max_tx_aggregation_subframes);
>
> + txq = sta->sta.txq[tid];
> + if (!amsdu && txq)
> + set_bit(IEEE80211_TXQ_NO_AMSDU, &to_txq_info(txq)->flags);
> +
> mutex_lock(&sta->ampdu_mlme.mtx);
>
> tid_tx = rcu_dereference_protected_tid_tx(sta, tid);
> diff --git a/net/mac80211/debugfs.c b/net/mac80211/debugfs.c
> index e433d0c..847779d 100644
> --- a/net/mac80211/debugfs.c
> +++ b/net/mac80211/debugfs.c
> @@ -127,6 +127,8 @@ static const char *hw_flag_names[NUM_IEEE80211_HW_FLAGS + 1] = {
> FLAG(BEACON_TX_STATUS),
> FLAG(NEEDS_UNIQUE_STA_ADDR),
> FLAG(SUPPORTS_REORDERING_BUFFER),
> + FLAG(TX_AMSDU),
> + FLAG(TX_FRAG_LIST),
>
> /* keep last for the build bug below */
> (void *)0x1
> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
> index a49c103..e68d8db 100644
> --- a/net/mac80211/ieee80211_i.h
> +++ b/net/mac80211/ieee80211_i.h
> @@ -799,6 +799,7 @@ struct mac80211_qos_map {
> enum txq_info_flags {
> IEEE80211_TXQ_STOP,
> IEEE80211_TXQ_AMPDU,
> + IEEE80211_TXQ_NO_AMSDU,
> };
>
> struct txq_info {
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 7bb67fa9..0c9cc6b 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -1324,6 +1324,10 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
> out:
> spin_unlock_bh(&txqi->queue.lock);
>
> + if (skb && skb_has_frag_list(skb) &&
> + !ieee80211_hw_check(&local->hw, TX_FRAG_LIST))
> + skb_linearize(skb);
> +
> return skb;
> }
> EXPORT_SYMBOL(ieee80211_tx_dequeue);
> @@ -2766,6 +2770,158 @@ void ieee80211_clear_fast_xmit(struct sta_info *sta)
> kfree_rcu(fast_tx, rcu_head);
> }
>
> +static int ieee80211_amsdu_pad(struct sk_buff *skb, int subframe_len)
> +{
> + int amsdu_len = subframe_len + sizeof(struct ethhdr);
> + int padding = (4 - amsdu_len) & 3;
> +
> + if (padding)
> + memset(skb_put(skb, padding), 0, padding);
> +
> + return padding;
> +}
> +
> +static bool ieee80211_amsdu_prepare_head(struct ieee80211_sub_if_data *sdata,
> + struct ieee80211_fast_tx *fast_tx,
> + struct sk_buff *skb)
> +{
> + struct ieee80211_local *local = sdata->local;
> + struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
> + struct ieee80211_hdr *hdr;
> + struct ethhdr amsdu_hdr;
> + int hdr_len = fast_tx->hdr_len - sizeof(rfc1042_header);
> + int subframe_len = skb->len - hdr_len;
> + void *data;
> + u8 *qc;
> +
> + if (info->control.flags & IEEE80211_TX_CTRL_AMSDU)
> + return true;
> +
> + if (skb_headroom(skb) < sizeof(amsdu_hdr) || skb_tailroom(skb) < 3) {
> + I802_DEBUG_INC(local->tx_expand_skb_head);
> +
> + if (pskb_expand_head(skb, sizeof(amsdu_hdr), 3, GFP_ATOMIC)) {
> + wiphy_debug(local->hw.wiphy,
> + "failed to reallocate TX buffer\n");
> + return false;
> + }
> + }
> +
> + subframe_len += ieee80211_amsdu_pad(skb, subframe_len);
> +
> + amsdu_hdr.h_proto = cpu_to_be16(subframe_len);
> + memcpy(amsdu_hdr.h_source, skb->data + fast_tx->sa_offs, ETH_ALEN);
> + memcpy(amsdu_hdr.h_dest, skb->data + fast_tx->da_offs, ETH_ALEN);
> +
> + data = skb_push(skb, sizeof(amsdu_hdr));
> + memmove(data, data + sizeof(amsdu_hdr), hdr_len);
> + memcpy(data + hdr_len, &amsdu_hdr, sizeof(amsdu_hdr));
> +
> + hdr = data;
> + qc = ieee80211_get_qos_ctl(hdr);
> + *qc |= IEEE80211_QOS_CTL_A_MSDU_PRESENT;
> +
> + info->control.flags |= IEEE80211_TX_CTRL_AMSDU;
> +
> + return true;
> +}
> +
> +static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
> + struct sta_info *sta,
> + struct ieee80211_fast_tx *fast_tx,
> + struct sk_buff *skb)
> +{
> + struct ieee80211_local *local = sdata->local;
> + u8 tid = skb->priority & IEEE80211_QOS_CTL_TAG1D_MASK;
> + struct ieee80211_txq *txq = sta->sta.txq[tid];
> + struct txq_info *txqi;
> + struct sk_buff **frag_tail, *head;
> + int subframe_len = skb->len - ETH_ALEN;
> + u8 max_subframes = sta->sta.max_amsdu_subframes;
> + int max_frags = local->hw.max_tx_fragments;
> + int max_amsdu_len;
> + __be16 len;
> + void *data;
> + bool ret = false;
> + int n = 1, nfrags;
> +
> + if (!ieee80211_hw_check(&local->hw, TX_AMSDU))
> + return false;
> +
> + if (!txq)
> + return false;
> +
> + txqi = to_txq_info(txq);
> + if (test_bit(IEEE80211_TXQ_NO_AMSDU, &txqi->flags))
> + return false;
> +
> + spin_lock_bh(&txqi->queue.lock);
> +
> + head = skb_peek_tail(&txqi->queue);
> + if (!head)
> + goto out;
> +
> + if (skb->len + head->len > max_amsdu_len)
> + goto out;
> +
> + /*
> + * HT A-MPDU limits maximum MPDU size to 4095 bytes. Since aggregation
> + * sessions are started/stopped without txq flush, use the limit here
> + * to avoid having to de-aggregate later.
> + */
> + if (skb->len + head->len > 4095 &&
> + !sta->sta.vht_cap.vht_supported)
> + goto out;
> +
> + if (!ieee80211_amsdu_prepare_head(sdata, fast_tx, head))
> + goto out;
> +
> + nfrags = 1 + skb_shinfo(skb)->nr_frags;
> + nfrags += 1 + skb_shinfo(head)->nr_frags;
> + frag_tail = &skb_shinfo(head)->frag_list;
> + while (*frag_tail) {
> + nfrags += 1 + skb_shinfo(*frag_tail)->nr_frags;
> + frag_tail = &(*frag_tail)->next;
> + n++;
> + }
> +
> + if (max_subframes && n > max_subframes)
> + goto out;
> +
> + if (max_frags && nfrags > max_frags)
> + goto out;
> +
> + if (skb_headroom(skb) < 8 || skb_tailroom(skb) < 3) {
> + I802_DEBUG_INC(local->tx_expand_skb_head);
> +
> + if (pskb_expand_head(skb, 8, 3, GFP_ATOMIC)) {
> + wiphy_debug(local->hw.wiphy,
> + "failed to reallocate TX buffer\n");
> + goto out;
> + }
> + }
> +
> + subframe_len += ieee80211_amsdu_pad(skb, subframe_len);
> +
> + ret = true;
> + data = skb_push(skb, ETH_ALEN + 2);
> + memmove(data, data + ETH_ALEN + 2, 2 * ETH_ALEN);
> +
> + data += 2 * ETH_ALEN;
> + len = cpu_to_be16(subframe_len);
> + memcpy(data, &len, 2);
> + memcpy(data + 2, rfc1042_header, ETH_ALEN);
> +
> + head->len += skb->len;
> + head->data_len += skb->len;
> + *frag_tail = skb;
> +
> +out:
> + spin_unlock_bh(&txqi->queue.lock);
> +
> + return ret;
> +}
> +
> static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
> struct net_device *dev, struct sta_info *sta,
> struct ieee80211_fast_tx *fast_tx,
> @@ -2820,6 +2976,10 @@ static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
>
> ieee80211_tx_stats(dev, skb->len + extra_head);
>
> + if ((hdr->frame_control & cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) &&
> + ieee80211_amsdu_aggregate(sdata, sta, fast_tx, skb))
> + return true;
> +
> /* will not be crypto-handled beyond what we do here, so use false
> * as the may-encrypt argument for the resize to not account for
> * more room than we already have in 'extra_head'
> --
> 2.2.2
>
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