netdev - Re: [WIP][PATCHES] Network xmit batching

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Date:	Mon, 02 Jul 2007 17:21:21 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"Matt Carlson" <mcarlson@...adcom.com>
cc:	hadi@...erus.ca, "Robert Olsson" <Robert.Olsson@...a.slu.se>,
	"Evgeniy Polyakov" <johnpol@....mipt.ru>,
	"Krishna Kumar2" <krkumar2@...ibm.com>,
	"Gagan Arneja" <gaagaan@...il.com>,
	"netdev" <netdev@...r.kernel.org>,
	"Rick Jones" <rick.jones2@...com>,
	"Sridhar Samudrala" <sri@...ibm.com>,
	"David Miller" <davem@...emloft.net>,
	"Jeff Garzik" <jeff@...zik.org>
Subject: Re: [WIP][PATCHES] Network xmit batching - tg3 support

On Mon, 2007-07-02 at 14:20 -0700, Matt Carlson wrote:

> 
> Also, I think the count, max_per_txd, and nr_frags fields of the
> tg3_tx_cbdata struct are not needed.

The count field is not needed also.

+struct tg3_tx_cbdata {
+	u32 base_flags;
+	int count;
+	unsigned int max_per_txd;
+	unsigned int nr_frags;
+	unsigned int mss;
+};
+#define TG3_SKB_CB(__skb)       ((struct tg3_tx_cbdata *)&((__skb)->cb[0]))

Only base_flags and mss are needed and these can be determined right
before sending the frame.  So is it better not to store these in the
skb->cb at all?

@@ -3118,12 +3120,16 @@ static void tg3_tx(struct tg3 *tp)
 	 */
 	smp_mb();
 
+	dcount = tg3_tx_avail(tp);
 	if (unlikely(netif_queue_stopped(tp->dev) &&
-		     (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH(tp)))) {
+		     (dcount > TG3_TX_WAKEUP_THRESH(tp)))) {
 		netif_tx_lock(tp->dev);
+		tp->dev->xmit_win = 1;
 		if (netif_queue_stopped(tp->dev) &&
-		    (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH(tp)))
+		    (dcount > TG3_TX_WAKEUP_THRESH(tp))) {
 			netif_wake_queue(tp->dev);
+			tp->dev->xmit_win = dcount;
+		}
 		netif_tx_unlock(tp->dev);
 	}
 }

This is also not right.  tg3_tx() runs without netif_tx_lock().
tg3_tx_avail() can change after you get the netif_tx_lock() and we must
get the updated value again.  If we just rely on dcount, we can call
wake_queue() when the ring is full, or there may be no wakeup when the
ring is empty.



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