On 2021-08-04 15:44, greearb@xxxxxxxxxxxxxxx wrote:
> From: Ben Greear <greearb@xxxxxxxxxxxxxxx>
>
> This improves performance when sending lots of frames that
> are requesting being mapped to a TXS callback.
>
> Add comments to help next person understood the tx path
> better.
>
> Signed-off-by: Ben Greear <greearb@xxxxxxxxxxxxxxx>
> ---
>
> v5: Rebased on top of previous series.
>
> drivers/net/wireless/mediatek/mt76/mt76.h | 48 +++++++---
> .../net/wireless/mediatek/mt76/mt7603/mac.c | 2 +-
> .../net/wireless/mediatek/mt76/mt7615/mac.c | 2 +-
> .../net/wireless/mediatek/mt76/mt76x02_mac.c | 2 +-
> .../net/wireless/mediatek/mt76/mt7915/mac.c | 8 +-
> .../net/wireless/mediatek/mt76/mt7921/mac.c | 9 +-
> drivers/net/wireless/mediatek/mt76/tx.c | 90 ++++++++++++++++---
> 7 files changed, 132 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> index 436bf2b8e2cd..016f563fec39 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> @@ -235,6 +235,14 @@ DECLARE_EWMA(signal, 10, 8);
> #define MT_WCID_TX_INFO_TXPWR_ADJ GENMASK(25, 18)
> #define MT_WCID_TX_INFO_SET BIT(31)
>
> +#define MT_PACKET_ID_MASK GENMASK(6, 0)
> +#define MT_PACKET_ID_NO_ACK 0
> +/* Request TXS, but don't try to match with skb. */
> +#define MT_PACKET_ID_NO_SKB 1
> +#define MT_PACKET_ID_FIRST 2
> +#define MT_PACKET_ID_HAS_RATE BIT(7)
> +#define MT_PACKET_ID_MAX (GENMASK(7, 0) - 1)
> +
> struct mt76_wcid {
> struct mt76_rx_tid __rcu *aggr[IEEE80211_NUM_TIDS];
>
> @@ -246,6 +254,8 @@ struct mt76_wcid {
>
> struct rate_info rate;
>
> + struct sk_buff *skb_status_array[MT_PACKET_ID_MAX + 1];
You could add this to reduce the struct size:
#define MT_NUM_STATUS_PACKETS \
(MT_PACKET_ID_MAX + 1 - MT_PACKET_ID_FIRST)
And then subtract MT_PACKET_ID_FIRST from cache entries.
> u16 idx;
> u8 hw_key_idx;
> u8 hw_key_idx2;
> @@ -302,13 +312,8 @@ struct mt76_rx_tid {
> #define MT_TX_CB_TXS_DONE BIT(1)
> #define MT_TX_CB_TXS_FAILED BIT(2)
>
> -#define MT_PACKET_ID_MASK GENMASK(6, 0)
> -#define MT_PACKET_ID_NO_ACK 0
> -#define MT_PACKET_ID_NO_SKB 1
> -#define MT_PACKET_ID_FIRST 2
> -#define MT_PACKET_ID_HAS_RATE BIT(7)
> -
> -#define MT_TX_STATUS_SKB_TIMEOUT HZ
> +/* This is timer for when to give up when waiting for TXS callback. */
> +#define MT_TX_STATUS_SKB_TIMEOUT (HZ / 8)
I think the way timeouts are checked now, HZ/8 is way too short.
I would recommend checking timeout only for packets where
MT_TX_CB_DMA_DONE is already set, and setting cb->jiffies from within
__mt76_tx_status_skb_done on DMA completion. That should make it
possible to keep the timeout short without running into it in cases
where significant congestion adds huge completion latency.
> @@ -1297,13 +1303,33 @@ mt76_token_put(struct mt76_dev *dev, int token)
> }
>
> static inline int
> -mt76_get_next_pkt_id(struct mt76_wcid *wcid)
> +mt76_get_next_pkt_id(struct mt76_dev *dev, struct mt76_wcid *wcid,
> + struct sk_buff *skb)
> {
> + struct sk_buff *qskb;
> +
> + lockdep_assert_held(&dev->status_list.lock);
> +
> wcid->packet_id = (wcid->packet_id + 1) & MT_PACKET_ID_MASK;
> - if (wcid->packet_id == MT_PACKET_ID_NO_ACK ||
> - wcid->packet_id == MT_PACKET_ID_NO_SKB)
> + if (wcid->packet_id < MT_PACKET_ID_FIRST)
> wcid->packet_id = MT_PACKET_ID_FIRST;
>
> + qskb = wcid->skb_status_array[wcid->packet_id];
> + if (qskb) {
> + /* bummer, already waiting on this pid. See if it is stale. */
> + struct mt76_tx_cb *cb = mt76_tx_skb_cb(qskb);
> +
> + if (!time_after(jiffies, cb->jiffies + MT_TX_STATUS_SKB_TIMEOUT)) {
> + /* ok, not stale. Increment pid anyway, will try next
> + * slot next time
> + */
> + return MT_PACKET_ID_NO_SKB;
> + }
> + }
> +
> + /* cache this skb for fast lookup by packet-id */
> + wcid->skb_status_array[wcid->packet_id] = skb;
> +
I think mt76_get_next_pkt_id is not a good place for caching the skb.
Better cache it in the same place that also puts the skb in the status
list: mt76_tx_status_skb_add
That way you can drop your (possibly broken) changes to mt7921, which
calls mt76_get_next_pkt_id directly, but does not support tx status
tracking for skbs.
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7915/mac.c b/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
> index d9f52e2611a7..8f5702981900 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
> @@ -1318,6 +1318,8 @@ mt7915_mac_add_txs_skb(struct mt7915_dev *dev, struct mt76_wcid *wcid, int pid,
>
> mt76_tx_status_lock(mdev, &list);
> skb = mt76_tx_status_skb_get(mdev, wcid, pid, &list);
> +
> + /* TODO: Gather stats anyway, even if we are not matching on an skb. */
Please drop this comment, since you're deleting in another patch in this
series anyway.
> @@ -1417,10 +1419,14 @@ mt7915_mac_add_txs_skb(struct mt7915_dev *dev, struct mt76_wcid *wcid, int pid,
> stats->tx_bw[0]++;
> break;
> }
> +
> + /* Cache rate for packets that don't get a TXS callback for some
> + * reason.
> + */
> wcid->rate = rate;
That comment is wrong, wcid->rate is cached because HE rates can't be
reported via skb->cb due to lack of space.
> diff --git a/drivers/net/wireless/mediatek/mt76/tx.c b/drivers/net/wireless/mediatek/mt76/tx.c
> index 6f302acb6e69..4c8504d3c904 100644
> --- a/drivers/net/wireless/mediatek/mt76/tx.c
> +++ b/drivers/net/wireless/mediatek/mt76/tx.c
> @@ -130,15 +154,30 @@ mt76_tx_status_skb_add(struct mt76_dev *dev, struct mt76_wcid *wcid,
> IEEE80211_TX_CTL_RATE_CTRL_PROBE)))
> return MT_PACKET_ID_NO_SKB;
>
> + /* due to limited range of the pktid (7 bits), we can only
> + * have a limited number of outstanding frames. I think it is OK to
> + * check the length outside of a lock since it doesn't matter too much
> + * if we read wrong data here.
> + * The TX-status callbacks don't always return a callback for an SKB,
> + * so the status_list may contain some stale skbs. Those will be cleaned
> + * out periodically, see MT_TX_STATUS_SKB_TIMEOUT.
> + */
> +
> + qlen = skb_queue_len(&dev->status_list);
> + if (qlen > 120)
> + return MT_PACKET_ID_NO_SKB;
Checking the length of the per-device status list doesn't make sense,
since pktid allocation is per-wcid.
- Felix
