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Fri, 13 Aug 2021 18:50:53 +0200 To: greearb@candelatech.com, linux-wireless@vger.kernel.org References: <20210804134505.3208-1-greearb@candelatech.com> From: Felix Fietkau Subject: Re: [PATCH v5 01/11] mt76: add hash lookup for skb on TXS status_list Message-ID: Date: Fri, 13 Aug 2021 18:50:53 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210804134505.3208-1-greearb@candelatech.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On 2021-08-04 15:44, greearb@candelatech.com wrote: > From: Ben Greear > > 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 > --- > > 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