linux-kernel - [PATCH 3.4 37/39] rt2800usb: slow down TX status polling

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Message-Id: <20131127005621.650741055@linuxfoundation.org>
Date:	Tue, 26 Nov 2013 16:57:01 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Stanislaw Gruszka <sgruszka@...hat.com>,
	"John W. Linville" <linville@...driver.com>
Subject: [PATCH 3.4 37/39] rt2800usb: slow down TX status polling

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislaw Gruszka <sgruszka@...hat.com>

commit 36165fd5b00bf8163f89c21bb16a3e9834555b10 upstream.

Polling TX statuses too frequently has two negative effects. First is
randomly peek CPU usage, causing overall system functioning delays.
Second bad effect is that device is not able to fill TX statuses in
H/W register on some workloads and we get lot of timeouts like below:

ieee80211 phy4: rt2800usb_entry_txstatus_timeout: Warning - TX status timeout for entry 7 in queue 2
ieee80211 phy4: rt2800usb_entry_txstatus_timeout: Warning - TX status timeout for entry 7 in queue 2
ieee80211 phy4: rt2800usb_txdone: Warning - Got TX status for an empty queue 2, dropping

This not only cause flood of messages in dmesg, but also bad throughput,
since rate scaling algorithm can not work optimally.

In the future, we should probably make polling interval be adjusted
automatically, but for now just increase values, this make mentioned
problems gone.

Resolve:
https://bugzilla.kernel.org/show_bug.cgi?id=62781

Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
Signed-off-by: John W. Linville <linville@...driver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/wireless/rt2x00/rt2800usb.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/net/wireless/rt2x00/rt2800usb.c
+++ b/drivers/net/wireless/rt2x00/rt2800usb.c
@@ -143,6 +143,8 @@ static bool rt2800usb_txstatus_timeout(s
 	return false;
 }
 
+#define TXSTATUS_READ_INTERVAL 1000000
+
 static bool rt2800usb_tx_sta_fifo_read_completed(struct rt2x00_dev *rt2x00dev,
 						 int urb_status, u32 tx_status)
 {
@@ -170,8 +172,9 @@ static bool rt2800usb_tx_sta_fifo_read_c
 		queue_work(rt2x00dev->workqueue, &rt2x00dev->txdone_work);
 
 	if (rt2800usb_txstatus_pending(rt2x00dev)) {
-		/* Read register after 250 us */
-		hrtimer_start(&rt2x00dev->txstatus_timer, ktime_set(0, 250000),
+		/* Read register after 1 ms */
+		hrtimer_start(&rt2x00dev->txstatus_timer,
+			      ktime_set(0, TXSTATUS_READ_INTERVAL),
 			      HRTIMER_MODE_REL);
 		return false;
 	}
@@ -196,8 +199,9 @@ static void rt2800usb_async_read_tx_stat
 	if (test_and_set_bit(TX_STATUS_READING, &rt2x00dev->flags))
 		return;
 
-	/* Read TX_STA_FIFO register after 500 us */
-	hrtimer_start(&rt2x00dev->txstatus_timer, ktime_set(0, 500000),
+	/* Read TX_STA_FIFO register after 2 ms */
+	hrtimer_start(&rt2x00dev->txstatus_timer,
+		      ktime_set(0, 2*TXSTATUS_READ_INTERVAL),
 		      HRTIMER_MODE_REL);
 }
 


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