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From:   Felix Fietkau <nbd@nbd.name>
To:     linux-wireless@vger.kernel.org
Subject: [PATCH v2 4/11] mt76: add utility functions for deferring work to a kernel thread
Date:   Tue, 15 Sep 2020 11:09:29 +0200
Message-Id: <20200915090929.4111-1-nbd@nbd.name>
In-Reply-To: <20200908211756.15998-4-nbd@nbd.name>
References: <20200908211756.15998-4-nbd@nbd.name>
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Sender: linux-wireless-owner@vger.kernel.org
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In order to avoid keeping work like tx scheduling pinned to the CPU it was
scheduled from, it makes sense to switch from tasklets to kernel threads.

Unlike a workqueue, this one only allows one fixed worker function to be
executed by the worker thread. Because of that, there is less locking
and less code for scheduling involved.
This is important because the tx worker is scheduled often in a hot path

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
v2: add more information to patch description

 drivers/net/wireless/mediatek/mt76/util.c | 28 +++++++++
 drivers/net/wireless/mediatek/mt76/util.h | 76 +++++++++++++++++++++++
 2 files changed, 104 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/util.c b/drivers/net/wireless/mediatek/mt76/util.c
index f53bb4ae5001..581964425468 100644
--- a/drivers/net/wireless/mediatek/mt76/util.c
+++ b/drivers/net/wireless/mediatek/mt76/util.c
@@ -110,4 +110,32 @@ int mt76_get_min_avg_rssi(struct mt76_dev *dev, bool ext_phy)
 }
 EXPORT_SYMBOL_GPL(mt76_get_min_avg_rssi);
 
+int __mt76_worker_fn(void *ptr)
+{
+	struct mt76_worker *w = ptr;
+
+	while (!kthread_should_stop()) {
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		if (kthread_should_park()) {
+			kthread_parkme();
+			continue;
+		}
+
+		if (!test_and_clear_bit(MT76_WORKER_SCHEDULED, &w->state)) {
+			schedule();
+			continue;
+		}
+
+		set_bit(MT76_WORKER_RUNNING, &w->state);
+		set_current_state(TASK_RUNNING);
+		w->fn(w);
+		cond_resched();
+		clear_bit(MT76_WORKER_RUNNING, &w->state);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__mt76_worker_fn);
+
 MODULE_LICENSE("Dual BSD/GPL");
diff --git a/drivers/net/wireless/mediatek/mt76/util.h b/drivers/net/wireless/mediatek/mt76/util.h
index fd1a68820e0a..1c363ea9ab9c 100644
--- a/drivers/net/wireless/mediatek/mt76/util.h
+++ b/drivers/net/wireless/mediatek/mt76/util.h
@@ -10,6 +10,19 @@
 #include <linux/skbuff.h>
 #include <linux/bitops.h>
 #include <linux/bitfield.h>
+#include <net/mac80211.h>
+
+struct mt76_worker
+{
+	struct task_struct *task;
+	void (*fn)(struct mt76_worker *);
+	unsigned long state;
+};
+
+enum {
+	MT76_WORKER_SCHEDULED,
+	MT76_WORKER_RUNNING,
+};
 
 #define MT76_INCR(_var, _size) \
 	(_var = (((_var) + 1) % (_size)))
@@ -45,4 +58,67 @@ mt76_skb_set_moredata(struct sk_buff *skb, bool enable)
 		hdr->frame_control &= ~cpu_to_le16(IEEE80211_FCTL_MOREDATA);
 }
 
+int __mt76_worker_fn(void *ptr);
+
+static inline int
+mt76_worker_setup(struct ieee80211_hw *hw, struct mt76_worker *w,
+		  void (*fn)(struct mt76_worker *),
+		  const char *name)
+{
+	const char *dev_name = wiphy_name(hw->wiphy);
+	int ret;
+
+	if (fn)
+		w->fn = fn;
+	w->task = kthread_create(__mt76_worker_fn, w, "mt76-%s %s",
+				 name, dev_name);
+
+	ret = PTR_ERR_OR_ZERO(w->task);
+	if (ret) {
+		w->task = NULL;
+		return ret;
+	}
+
+	wake_up_process(w->task);
+
+	return 0;
+}
+
+static inline void mt76_worker_schedule(struct mt76_worker *w)
+{
+	if (!w->task)
+		return;
+
+	if (!test_and_set_bit(MT76_WORKER_SCHEDULED, &w->state) &&
+	    !test_bit(MT76_WORKER_RUNNING, &w->state))
+		wake_up_process(w->task);
+}
+
+static inline void mt76_worker_disable(struct mt76_worker *w)
+{
+	if (!w->task)
+		return;
+
+	kthread_park(w->task);
+	WRITE_ONCE(w->state, 0);
+}
+
+static inline void mt76_worker_enable(struct mt76_worker *w)
+{
+	if (!w->task)
+		return;
+
+	kthread_unpark(w->task);
+	mt76_worker_schedule(w);
+}
+
+static inline void mt76_worker_teardown(struct mt76_worker *w)
+{
+	if (!w->task)
+		return;
+
+	kthread_stop(w->task);
+	w->task = NULL;
+}
+
 #endif
-- 
2.28.0