From:   David Mosberger-Tang <davidm@egauge.net>
Subject: [PATCH v2 02/50] wilc1000: switch txq_event from completion to
 waitqueue
Date:   Thu, 23 Dec 2021 01:14:05 +0000 (UTC)
Message-Id: <20211223011358.4031459-3-davidm@egauge.net>
In-Reply-To: <20211223011358.4031459-1-davidm@egauge.net>
References: <20211223011358.4031459-1-davidm@egauge.net>
MIME-Version: 1.0
To:     Ajay Singh <ajay.kathat@microchip.com>
Cc:     Claudiu Beznea <claudiu.beznea@microchip.com>,
        Kalle Valo <kvalo@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        David Mosberger-Tang <davidm@egauge.net>
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Precedence: bulk

Completion structs are essentially counting semaphores: every
complete() call wakes up exactly one thread, either immediately (when
there are waiters queued) or in the future (when a waiter arrives).
This isn't really the appropriate synchronization structure for the
wilc1000 transmit queue handler (wilc_wlan_handle_txq) because it will
consume zero, one, or more packets on each call.  Instead, use a
waitqueue as a condition variable: wake_up_interruptible() wakes up
the tx queue handler from a call to wait_event_interruptible()
whenever something interesting happens and it then takes the
appropriate action.  This has a couple of benefits:

 - Since the transmit queue handler often transfers multiple packets
   to the chip on each call, repeated calls to wait_for_completion()
   when there is no actual work to do are avoided.

 - When the transmit queue handler cannot transfer any packets at all,
   it'll simply give up the current time slice and then tries again.
   Previously, the transmit would stall until a new packet showed up
   (which potentially could cause extended stalls).  It would be even
   better to wait for a "tx queue not full" interrupt but, sadly, I'm
   told the wilc1000 firmware doesn't provide that.

 - There is no longer any need for wilc_wlan_txq_filter_dup_tcp_ack()
   to adjust the completion structs wait count by calling
   wait_for_completion_timeout() for each dropped packet.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
---
 drivers/net/wireless/microchip/wilc1000/cfg80211.c |  2 +-
 drivers/net/wireless/microchip/wilc1000/netdev.c   | 13 +++++++++----
 drivers/net/wireless/microchip/wilc1000/netdev.h   |  2 +-
 drivers/net/wireless/microchip/wilc1000/wlan.c     | 12 ++----------
 4 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/net/wireless/microchip/wilc1000/cfg80211.c b/drivers/net/wireless/microchip/wilc1000/cfg80211.c
index 8d8378bafd9b0..be387a8abb6af 100644
--- a/drivers/net/wireless/microchip/wilc1000/cfg80211.c
+++ b/drivers/net/wireless/microchip/wilc1000/cfg80211.c
@@ -1692,7 +1692,7 @@ static void wlan_init_locks(struct wilc *wl)
 	spin_lock_init(&wl->txq_spinlock);
 	mutex_init(&wl->txq_add_to_head_cs);
 
-	init_completion(&wl->txq_event);
+	init_waitqueue_head(&wl->txq_event);
 	init_completion(&wl->cfg_event);
 	init_completion(&wl->sync_event);
 	init_completion(&wl->txq_thread_started);
diff --git a/drivers/net/wireless/microchip/wilc1000/netdev.c b/drivers/net/wireless/microchip/wilc1000/netdev.c
index 643bddaae32ad..d5969f2e369c4 100644
--- a/drivers/net/wireless/microchip/wilc1000/netdev.c
+++ b/drivers/net/wireless/microchip/wilc1000/netdev.c
@@ -144,10 +144,12 @@ static int wilc_txq_task(void *vp)
 	int ret;
 	u32 txq_count;
 	struct wilc *wl = vp;
+	long timeout;
 
 	complete(&wl->txq_thread_started);
 	while (1) {
-		wait_for_completion(&wl->txq_event);
+		wait_event_interruptible(wl->txq_event,
+					 (wl->txq_entries > 0 || wl->close));
 
 		if (wl->close) {
 			complete(&wl->txq_thread_started);
@@ -170,6 +172,11 @@ static int wilc_txq_task(void *vp)
 				}
 				srcu_read_unlock(&wl->srcu, srcu_idx);
 			}
+			if (ret == WILC_VMM_ENTRY_FULL_RETRY) {
+				timeout = msecs_to_jiffies(1);
+				set_current_state(TASK_INTERRUPTIBLE);
+				schedule_timeout(timeout);
+			}
 		} while (ret == WILC_VMM_ENTRY_FULL_RETRY && !wl->close);
 	}
 	return 0;
@@ -419,12 +426,11 @@ static void wlan_deinitialize_threads(struct net_device *dev)
 
 	wl->close = 1;
 
-	complete(&wl->txq_event);
-
 	if (wl->txq_thread) {
 		kthread_stop(wl->txq_thread);
 		wl->txq_thread = NULL;
 	}
+	wake_up_interruptible(&wl->txq_event);
 }
 
 static void wilc_wlan_deinitialize(struct net_device *dev)
@@ -446,7 +452,6 @@ static void wilc_wlan_deinitialize(struct net_device *dev)
 			wl->hif_func->disable_interrupt(wl);
 			mutex_unlock(&wl->hif_cs);
 		}
-		complete(&wl->txq_event);
 
 		wlan_deinitialize_threads(dev);
 		deinit_irq(dev);
diff --git a/drivers/net/wireless/microchip/wilc1000/netdev.h b/drivers/net/wireless/microchip/wilc1000/netdev.h
index f4fc2cc392bd0..c07f58a86bc76 100644
--- a/drivers/net/wireless/microchip/wilc1000/netdev.h
+++ b/drivers/net/wireless/microchip/wilc1000/netdev.h
@@ -237,7 +237,7 @@ struct wilc {
 
 	struct completion cfg_event;
 	struct completion sync_event;
-	struct completion txq_event;
+	wait_queue_head_t txq_event;
 	struct completion txq_thread_started;
 
 	struct task_struct *txq_thread;
diff --git a/drivers/net/wireless/microchip/wilc1000/wlan.c b/drivers/net/wireless/microchip/wilc1000/wlan.c
index c4da14147dd04..26fa7078acffd 100644
--- a/drivers/net/wireless/microchip/wilc1000/wlan.c
+++ b/drivers/net/wireless/microchip/wilc1000/wlan.c
@@ -75,7 +75,7 @@ static void wilc_wlan_txq_add_to_tail(struct net_device *dev, u8 q_num,
 
 	spin_unlock_irqrestore(&wilc->txq_spinlock, flags);
 
-	complete(&wilc->txq_event);
+	wake_up_interruptible(&wilc->txq_event);
 }
 
 static void wilc_wlan_txq_add_to_head(struct wilc_vif *vif, u8 q_num,
@@ -94,7 +94,7 @@ static void wilc_wlan_txq_add_to_head(struct wilc_vif *vif, u8 q_num,
 
 	spin_unlock_irqrestore(&wilc->txq_spinlock, flags);
 	mutex_unlock(&wilc->txq_add_to_head_cs);
-	complete(&wilc->txq_event);
+	wake_up_interruptible(&wilc->txq_event);
 }
 
 #define NOT_TCP_ACK			(-1)
@@ -196,7 +196,6 @@ static void wilc_wlan_txq_filter_dup_tcp_ack(struct net_device *dev)
 	struct wilc *wilc = vif->wilc;
 	struct tcp_ack_filter *f = &vif->ack_filter;
 	u32 i = 0;
-	u32 dropped = 0;
 	unsigned long flags;
 
 	spin_lock_irqsave(&wilc->txq_spinlock, flags);
@@ -226,7 +225,6 @@ static void wilc_wlan_txq_filter_dup_tcp_ack(struct net_device *dev)
 					tqe->tx_complete_func(tqe->priv,
 							      tqe->status);
 				kfree(tqe);
-				dropped++;
 			}
 		}
 	}
@@ -239,12 +237,6 @@ static void wilc_wlan_txq_filter_dup_tcp_ack(struct net_device *dev)
 		f->pending_base = 0;
 
 	spin_unlock_irqrestore(&wilc->txq_spinlock, flags);
-
-	while (dropped > 0) {
-		wait_for_completion_timeout(&wilc->txq_event,
-					    msecs_to_jiffies(1));
-		dropped--;
-	}
 }
 
 void wilc_enable_tcp_ack_filter(struct wilc_vif *vif, bool value)
-- 
2.25.1