Re: pktgen terminating condition

Re: pktgen terminating condition

[Daniele Venzano]

----- Message d'origine -----
De: jamal <hadi@cyberus.ca>
Date: Fri, 31 Aug 2007 09:50:03 -0400
Sujet: Re: Re: pktgen terminating condition

>I dont know if you followed the discussion - by defering the freeing of
>skbs, you will be slowing down socket apps sending from the local
>machine. It may be ok if the socket buffers were huge, but that comes at
>the cost of system memory (which may not be a big deal)
>Do you by any chance recall why you used the idle interupt instead of
>txok to kick the prunning of tx descriptors?

That should be asked to the original author of the driver, that I wasn't able to contact when I took over the maintainership several years ago.
I think that since this chip is usually used on cheap/low performance (relatively speaking) devices it was felt that generating an interrupt for each transmitted packet was going to affect the performance of the system too much. At the start, if I remember correctly, this was a chip thought for consumer use, where transmissions won't happen continuously for long periods of time. Then the sis900 started to get used everywhere, from embedded systems to (cheap) server motherboards and the usage scenario changed.


--
Daniele Venzano
venza@brownhat.org

[PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[Mandeep Singh Baines]

[-- Attachment #1: Type: text/plain, Size: 2045 bytes --]

Hi Daniele,

Attached is a patch for converting the sis900 driver to NAPI. Please take a
look at let me know what you think. I'm not 100% sure if I'm handling the 
rotting packet issue correctly or that I have the locking right in tx_timeout.
These might be areas to look at closely.

I didn't see much saving in interrupts on my machine (too fast, I guess). But
I still think its beneficial: pushing work out of the interrupt handler into
a bottom half is a good thing and we no longer need to disable interrupts 
in start_xmit. 

I did see a significant boost to tx performance by optimizing start_xmit: more
than double pps in pktgen.

I'm also attaching some test results for various iterations of development.

Regards,
Mandeep

Daniele Venzano (venza@brownhat.org) wrote:
> ----- Message d'origine -----
> De: jamal <hadi@cyberus.ca>
> Date: Fri, 31 Aug 2007 09:50:03 -0400
> Sujet: Re: Re: pktgen terminating condition
> 
> >I dont know if you followed the discussion - by defering the freeing of
> >skbs, you will be slowing down socket apps sending from the local
> >machine. It may be ok if the socket buffers were huge, but that comes at
> >the cost of system memory (which may not be a big deal)
> >Do you by any chance recall why you used the idle interupt instead of
> >txok to kick the prunning of tx descriptors?
> 
> That should be asked to the original author of the driver, that I wasn't able to contact when I took over the maintainership several years ago.
> I think that since this chip is usually used on cheap/low performance (relatively speaking) devices it was felt that generating an interrupt for each transmitted packet was going to affect the performance of the system too much. At the start, if I remember correctly, this was a chip thought for consumer use, where transmissions won't happen continuously for long periods of time. Then the sis900 started to get used everywhere, from embedded systems to (cheap) server motherboards and the usage scenario changed.
> 
> 
> --
> Daniele Venzano
> venza@brownhat.org

[-- Attachment #2: sis900_testing.txt --]
[-- Type: text/plain, Size: 1296 bytes --]

Tested using pktgen.

cpuinfo:
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 8
model name      : AMD Geode NX
stepping        : 1
cpu MHz         : 1397.641
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mp mmxext 3dnowext 3dnow ts fid vid
bogomips        : 2796.00
clflush size    : 32

meminfo:
MemTotal:       907092 kB


Results in pps. Sending 400000 60-byte packets.
Other than Iteration 5 and 6, there is 1 interrupt per packet.

Iteration 0 (replace TxIDLE with TxOK):
62222, 62052, 62335

Iteration 1 (optimize sis900_start_xmit):
148815, 148815, 148829

Iteration 2 (convert Rx to NAPI):
148669, 148635, 148677

Iteration 3 (remove tx_full dev state variable):
148677, 148528, 148532

Iteration 4 (optimize finish_xmit):
148677, 148676, 148689

Iteration 5 (move tx completion code into NAPI poll):
147751, 147658, 147809
Interrupts:
359270, 360747, 358010

Iteration 6 (cleanup + rotting packet handling + rx optimization):
148652, 148680, 148681
Interrupts:
399927, 399841, 399835


[-- Attachment #3: sis900_napi.patch --]
[-- Type: text/plain, Size: 19790 bytes --]

diff --git a/drivers/net/sis900.c b/drivers/net/sis900.c
index 7c6e480..862e15a 100644
--- a/drivers/net/sis900.c
+++ b/drivers/net/sis900.c
@@ -185,7 +185,6 @@ struct sis900_private {
 	dma_addr_t tx_ring_dma;
 	dma_addr_t rx_ring_dma;
 
-	unsigned int tx_full; /* The Tx queue is full. */
 	u8 host_bridge_rev;
 	u8 chipset_rev;
 };
@@ -202,8 +201,10 @@ MODULE_PARM_DESC(max_interrupt_work, "SiS 900/7016 maximum events handled per in
 MODULE_PARM_DESC(sis900_debug, "SiS 900/7016 bitmapped debugging message level");
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-static void sis900_poll(struct net_device *dev);
+static void sis900_poll_controller(struct net_device *dev);
 #endif
+
+static int sis900_poll(struct net_device *dev, int *budget);
 static int sis900_open(struct net_device *net_dev);
 static int sis900_mii_probe (struct net_device * net_dev);
 static void sis900_init_rxfilter (struct net_device * net_dev);
@@ -216,8 +217,8 @@ static void sis900_tx_timeout(struct net_device *net_dev);
 static void sis900_init_tx_ring(struct net_device *net_dev);
 static void sis900_init_rx_ring(struct net_device *net_dev);
 static int sis900_start_xmit(struct sk_buff *skb, struct net_device *net_dev);
-static int sis900_rx(struct net_device *net_dev);
-static void sis900_finish_xmit (struct net_device *net_dev);
+static int sis900_rx(struct net_device *net_dev, int limit);
+static int sis900_finish_xmit (struct net_device *net_dev);
 static irqreturn_t sis900_interrupt(int irq, void *dev_instance);
 static int sis900_close(struct net_device *net_dev);
 static int mii_ioctl(struct net_device *net_dev, struct ifreq *rq, int cmd);
@@ -474,9 +475,11 @@ static int __devinit sis900_probe(struct pci_dev *pci_dev,
 	net_dev->tx_timeout = sis900_tx_timeout;
 	net_dev->watchdog_timeo = TX_TIMEOUT;
 	net_dev->ethtool_ops = &sis900_ethtool_ops;
+	net_dev->poll = &sis900_poll;
+	net_dev->weight = 64;
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-        net_dev->poll_controller = &sis900_poll;
+        net_dev->poll_controller = &sis900_poll_controller;
 #endif
 
 	if (sis900_debug > 0)
@@ -979,13 +982,44 @@ static u16 sis900_reset_phy(struct net_device *net_dev, int phy_addr)
 	return status;
 }
 
+static int sis900_poll(struct net_device *dev, int *budget)
+{
+	struct sis900_private *sis_priv = dev->priv;
+	long ioaddr = dev->base_addr;
+	int limit = min_t(int, dev->quota, *budget);
+	int rx_work_done;
+	int tx_work_done;
+
+	/* run TX completion thread */
+	spin_lock(sis_priv->lock);
+	tx_work_done = sis900_finish_xmit(dev);
+	spin_unlock(sis_priv->lock);
+
+	/* run RX thread */
+	rx_work_done = sis900_rx(dev, limit);
+	*budget -= rx_work_done;
+	dev->quota -= rx_work_done;
+
+	/* re-enable interrupts if no work done */
+	if (rx_work_done + tx_work_done == 0) {
+		netif_rx_complete(dev);
+		/* Enable all known interrupts. */
+		outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
+		/* Handle rotting packet */
+		sis900_rx(dev, NUM_RX_DESC);
+		return 0;
+	}
+
+	return 1;
+}
+
 #ifdef CONFIG_NET_POLL_CONTROLLER
 /*
  * Polling 'interrupt' - used by things like netconsole to send skbs
  * without having to re-enable interrupts. It's not called while
  * the interrupt routine is executing.
 */
-static void sis900_poll(struct net_device *dev)
+static void sis900_poll_controller(struct net_device *dev)
 {
 	disable_irq(dev->irq);
 	sis900_interrupt(dev->irq, dev);
@@ -1032,7 +1066,7 @@ sis900_open(struct net_device *net_dev)
 	sis900_set_mode(ioaddr, HW_SPEED_10_MBPS, FDX_CAPABLE_HALF_SELECTED);
 
 	/* Enable all known interrupts by setting the interrupt mask. */
-	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxIDLE), ioaddr + imr);
+	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
 	outl(RxENA | inl(ioaddr + cr), ioaddr + cr);
 	outl(IE, ioaddr + ier);
 
@@ -1102,7 +1136,6 @@ sis900_init_tx_ring(struct net_device *net_dev)
 	long ioaddr = net_dev->base_addr;
 	int i;
 
-	sis_priv->tx_full = 0;
 	sis_priv->dirty_tx = sis_priv->cur_tx = 0;
 
 	for (i = 0; i < NUM_TX_DESC; i++) {
@@ -1517,7 +1550,6 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 {
 	struct sis900_private *sis_priv = net_dev->priv;
 	long ioaddr = net_dev->base_addr;
-	unsigned long flags;
 	int i;
 
 	if(netif_msg_tx_err(sis_priv))
@@ -1527,8 +1559,8 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 	/* Disable interrupts by clearing the interrupt mask. */
 	outl(0x0000, ioaddr + imr);
 
-	/* use spinlock to prevent interrupt handler accessing buffer ring */
-	spin_lock_irqsave(&sis_priv->lock, flags);
+	/* use spinlock to prevent bh from accessing buffer ring */
+	spin_lock_bh(&sis_priv->lock);
 
 	/* discard unsent packets */
 	sis_priv->dirty_tx = sis_priv->cur_tx = 0;
@@ -1546,10 +1578,9 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 			sis_priv->stats.tx_dropped++;
 		}
 	}
-	sis_priv->tx_full = 0;
 	netif_wake_queue(net_dev);
 
-	spin_unlock_irqrestore(&sis_priv->lock, flags);
+	spin_unlock_bh(&sis_priv->lock);
 
 	net_dev->trans_start = jiffies;
 
@@ -1557,7 +1588,7 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 	outl(sis_priv->tx_ring_dma, ioaddr + txdp);
 
 	/* Enable all known interrupts by setting the interrupt mask. */
-	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxIDLE), ioaddr + imr);
+	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
 	return;
 }
 
@@ -1574,52 +1605,27 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 static int
 sis900_start_xmit(struct sk_buff *skb, struct net_device *net_dev)
 {
-	struct sis900_private *sis_priv = net_dev->priv;
 	long ioaddr = net_dev->base_addr;
-	unsigned int  entry;
-	unsigned long flags;
-	unsigned int  index_cur_tx, index_dirty_tx;
-	unsigned int  count_dirty_tx;
+	struct sis900_private *sis_priv = net_dev->priv;
+        unsigned int entry;
 
-	/* Don't transmit data before the complete of auto-negotiation */
-	if(!sis_priv->autong_complete){
+	/* Don't transmit data before auto-negotiation is complete */
+	if(unlikely(!sis_priv->autong_complete)){
 		netif_stop_queue(net_dev);
 		return 1;
 	}
 
-	spin_lock_irqsave(&sis_priv->lock, flags);
-
-	/* Calculate the next Tx descriptor entry. */
-	entry = sis_priv->cur_tx % NUM_TX_DESC;
+	/* Set the Tx descriptor and enable Transmit State Machine */
+        entry = sis_priv->cur_tx++ % NUM_TX_DESC;
 	sis_priv->tx_skbuff[entry] = skb;
-
-	/* set the transmit buffer descriptor and enable Transmit State Machine */
 	sis_priv->tx_ring[entry].bufptr = pci_map_single(sis_priv->pci_dev,
 		skb->data, skb->len, PCI_DMA_TODEVICE);
 	sis_priv->tx_ring[entry].cmdsts = (OWN | skb->len);
 	outl(TxENA | inl(ioaddr + cr), ioaddr + cr);
 
-	sis_priv->cur_tx ++;
-	index_cur_tx = sis_priv->cur_tx;
-	index_dirty_tx = sis_priv->dirty_tx;
-
-	for (count_dirty_tx = 0; index_cur_tx != index_dirty_tx; index_dirty_tx++)
-		count_dirty_tx ++;
-
-	if (index_cur_tx == index_dirty_tx) {
-		/* dirty_tx is met in the cycle of cur_tx, buffer full */
-		sis_priv->tx_full = 1;
-		netif_stop_queue(net_dev);
-	} else if (count_dirty_tx < NUM_TX_DESC) {
-		/* Typical path, tell upper layer that more transmission is possible */
-		netif_start_queue(net_dev);
-	} else {
-		/* buffer full, tell upper layer no more transmission */
-		sis_priv->tx_full = 1;
+        /* If Tx ring is full, tell upper layer no more transmission */
+	if (unlikely(sis_priv->cur_tx - sis_priv->dirty_tx >= NUM_TX_DESC))
 		netif_stop_queue(net_dev);
-	}
-
-	spin_unlock_irqrestore(&sis_priv->lock, flags);
 
 	net_dev->trans_start = jiffies;
 
@@ -1650,32 +1656,27 @@ static irqreturn_t sis900_interrupt(int irq, void *dev_instance)
 	u32 status;
 	unsigned int handled = 0;
 
-	spin_lock (&sis_priv->lock);
-
-	do {
-		status = inl(ioaddr + isr);
-
-		if ((status & (HIBERR|TxURN|TxERR|TxIDLE|RxORN|RxERR|RxOK)) == 0)
-			/* nothing intresting happened */
-			break;
+	while ((status = inl(ioaddr + isr))) {
 		handled = 1;
 
-		/* why dow't we break after Tx/Rx case ?? keyword: full-duplex */
-		if (status & (RxORN | RxERR | RxOK))
-			/* Rx interrupt */
-			sis900_rx(net_dev);
+		/* why don't we break after Tx/Rx case ?? 
+		 * keyword: full-duplex 
+		 */
 
-		if (status & (TxURN | TxERR | TxIDLE))
-			/* Tx interrupt */
-			sis900_finish_xmit(net_dev);
+		/* Rx interrupt */
+                if (status & (TxURN|TxERR|TxOK|RxORN|RxERR|RxOK)) {
+			/* Disable all interrupts. */
+			outl(0, ioaddr + imr);
+			netif_rx_schedule(net_dev);
+		}
 
 		/* something strange happened !!! */
-		if (status & HIBERR) {
+		if (status & HIBERR)
 			if(netif_msg_intr(sis_priv))
 				printk(KERN_INFO "%s: Abnormal interrupt,"
-					"status %#8.8x.\n", net_dev->name, status);
-			break;
-		}
+					"status %#8.8x.\n", 
+					net_dev->name, status);
+
 		if (--boguscnt < 0) {
 			if(netif_msg_intr(sis_priv))
 				printk(KERN_INFO "%s: Too much work at interrupt, "
@@ -1683,14 +1684,13 @@ static irqreturn_t sis900_interrupt(int irq, void *dev_instance)
 					net_dev->name, status);
 			break;
 		}
-	} while (1);
+	}
 
 	if(netif_msg_intr(sis_priv))
 		printk(KERN_DEBUG "%s: exiting interrupt, "
 		       "interrupt status = 0x%#8.8x.\n",
 		       net_dev->name, inl(ioaddr + isr));
 
-	spin_unlock (&sis_priv->lock);
 	return IRQ_RETVAL(handled);
 }
 
@@ -1704,25 +1704,29 @@ static irqreturn_t sis900_interrupt(int irq, void *dev_instance)
  *	don't do "too much" work here
  */
 
-static int sis900_rx(struct net_device *net_dev)
+static int sis900_rx(struct net_device *net_dev, int limit)
 {
 	struct sis900_private *sis_priv = net_dev->priv;
+	struct net_device_stats *stats = &sis_priv->stats;
 	long ioaddr = net_dev->base_addr;
-	unsigned int entry = sis_priv->cur_rx % NUM_RX_DESC;
-	u32 rx_status = sis_priv->rx_ring[entry].cmdsts;
-	int rx_work_limit;
+	int cur_rx = sis_priv->cur_rx;
+	int dirty_rx, orig_dirty_rx = sis_priv->dirty_rx;
+	int count;
 
 	if (netif_msg_rx_status(sis_priv))
-		printk(KERN_DEBUG "sis900_rx, cur_rx:%4.4d, dirty_rx:%4.4d "
-		       "status:0x%8.8x\n",
-		       sis_priv->cur_rx, sis_priv->dirty_rx, rx_status);
-	rx_work_limit = sis_priv->dirty_rx + NUM_RX_DESC - sis_priv->cur_rx;
+		printk(KERN_DEBUG "sis900_rx, cur_rx:%4.4d, dirty_rx:%4.4d\n",
+		       cur_rx, orig_dirty_rx);
 
-	while (rx_status & OWN) {
+	for (count = 0; count < limit; cur_rx++, count++) {
+		unsigned int entry;
+		u32 rx_status;
 		unsigned int rx_size;
 		unsigned int data_size;
 
-		if (--rx_work_limit < 0)
+		entry = cur_rx % NUM_RX_DESC;
+		rx_status = sis_priv->rx_ring[entry].cmdsts;
+
+		if ((rx_status & OWN) == 0)
 			break;
 
 		data_size = rx_status & DSIZE;
@@ -1735,113 +1739,71 @@ static int sis900_rx(struct net_device *net_dev)
 #endif
 
 		if (rx_status & (ABORT|OVERRUN|TOOLONG|RUNT|RXISERR|CRCERR|FAERR)) {
-			/* corrupted packet received */
-			if (netif_msg_rx_err(sis_priv))
-				printk(KERN_DEBUG "%s: Corrupted packet "
-				       "received, buffer status = 0x%8.8x/%d.\n",
-				       net_dev->name, rx_status, data_size);
-			sis_priv->stats.rx_errors++;
+			pci_unmap_single(sis_priv->pci_dev,
+				sis_priv->rx_ring[entry].bufptr, RX_BUF_SIZE,
+				PCI_DMA_FROMDEVICE);
+			dev_kfree_skb(sis_priv->rx_skbuff[entry]);
+
+			stats->rx_errors++;
 			if (rx_status & OVERRUN)
-				sis_priv->stats.rx_over_errors++;
+				stats->rx_over_errors++;
 			if (rx_status & (TOOLONG|RUNT))
-				sis_priv->stats.rx_length_errors++;
+				stats->rx_length_errors++;
 			if (rx_status & (RXISERR | FAERR))
-				sis_priv->stats.rx_frame_errors++;
+				stats->rx_frame_errors++;
 			if (rx_status & CRCERR)
-				sis_priv->stats.rx_crc_errors++;
-			/* reset buffer descriptor state */
-			sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
+				stats->rx_crc_errors++;
 		} else {
 			struct sk_buff * skb;
-			struct sk_buff * rx_skb;
 
 			pci_unmap_single(sis_priv->pci_dev,
 				sis_priv->rx_ring[entry].bufptr, RX_BUF_SIZE,
 				PCI_DMA_FROMDEVICE);
 
-			/* refill the Rx buffer, what if there is not enought
-			 * memory for new socket buffer ?? */
-			if ((skb = dev_alloc_skb(RX_BUF_SIZE)) == NULL) {
-				/*
-				 * Not enough memory to refill the buffer
-				 * so we need to recycle the old one so
-				 * as to avoid creating a memory hole
-				 * in the rx ring
-				 */
-				skb = sis_priv->rx_skbuff[entry];
-				sis_priv->stats.rx_dropped++;
-				goto refill_rx_ring;
-			}	
-
-			/* This situation should never happen, but due to
-			   some unknow bugs, it is possible that
-			   we are working on NULL sk_buff :-( */
-			if (sis_priv->rx_skbuff[entry] == NULL) {
-				if (netif_msg_rx_err(sis_priv))
-					printk(KERN_WARNING "%s: NULL pointer "
-					      "encountered in Rx ring\n"
-					      "cur_rx:%4.4d, dirty_rx:%4.4d\n",
-					      net_dev->name, sis_priv->cur_rx,
-					      sis_priv->dirty_rx);
-				break;
-			}
-
 			/* give the socket buffer to upper layers */
-			rx_skb = sis_priv->rx_skbuff[entry];
-			skb_put(rx_skb, rx_size);
-			rx_skb->protocol = eth_type_trans(rx_skb, net_dev);
-			netif_rx(rx_skb);
+			skb = sis_priv->rx_skbuff[entry];
+			skb_put(skb, rx_size);
+			skb->protocol = eth_type_trans(skb, net_dev);
+			netif_receive_skb(skb);
 
 			/* some network statistics */
 			if ((rx_status & BCAST) == MCAST)
-				sis_priv->stats.multicast++;
+				stats->multicast++;
 			net_dev->last_rx = jiffies;
-			sis_priv->stats.rx_bytes += rx_size;
-			sis_priv->stats.rx_packets++;
-			sis_priv->dirty_rx++;
-refill_rx_ring:
-			sis_priv->rx_skbuff[entry] = skb;
-			sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
-                	sis_priv->rx_ring[entry].bufptr =
-				pci_map_single(sis_priv->pci_dev, skb->data,
-					RX_BUF_SIZE, PCI_DMA_FROMDEVICE);
+			stats->rx_bytes += rx_size;
+			stats->rx_packets++;
 		}
-		sis_priv->cur_rx++;
-		entry = sis_priv->cur_rx % NUM_RX_DESC;
-		rx_status = sis_priv->rx_ring[entry].cmdsts;
-	} // while
+	}
 
-	/* refill the Rx buffer, what if the rate of refilling is slower
-	 * than consuming ?? */
-	for (; sis_priv->cur_rx != sis_priv->dirty_rx; sis_priv->dirty_rx++) {
+	/* refill the Rx ring. */
+	for (dirty_rx = orig_dirty_rx; dirty_rx < cur_rx; dirty_rx++) {
 		struct sk_buff *skb;
+		unsigned int entry;
 
-		entry = sis_priv->dirty_rx % NUM_RX_DESC;
-
-		if (sis_priv->rx_skbuff[entry] == NULL) {
-			if ((skb = dev_alloc_skb(RX_BUF_SIZE)) == NULL) {
-				/* not enough memory for skbuff, this makes a
-				 * "hole" on the buffer ring, it is not clear
-				 * how the hardware will react to this kind
-				 * of degenerated buffer */
-				if (netif_msg_rx_err(sis_priv))
-					printk(KERN_INFO "%s: Memory squeeze,"
-						"deferring packet.\n",
-						net_dev->name);
-				sis_priv->stats.rx_dropped++;
-				break;
-			}
-			sis_priv->rx_skbuff[entry] = skb;
-			sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
-                	sis_priv->rx_ring[entry].bufptr =
-				pci_map_single(sis_priv->pci_dev, skb->data,
-					RX_BUF_SIZE, PCI_DMA_FROMDEVICE);
+		if ((skb = dev_alloc_skb(RX_BUF_SIZE)) == NULL) {
+			if (netif_msg_rx_err(sis_priv))
+				printk(KERN_INFO "%s: Memory squeeze,"
+					"deferring packet.\n",
+					net_dev->name);
+			break;
 		}
+
+		entry = dirty_rx % NUM_RX_DESC;
+		sis_priv->rx_skbuff[entry] = skb;
+		sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
+               	sis_priv->rx_ring[entry].bufptr =
+			pci_map_single(sis_priv->pci_dev, skb->data,
+				RX_BUF_SIZE, PCI_DMA_FROMDEVICE);
 	}
+
 	/* re-enable the potentially idle receive state matchine */
-	outl(RxENA | inl(ioaddr + cr), ioaddr + cr );
+	if (dirty_rx != orig_dirty_rx)
+		outl(RxENA | inl(ioaddr + cr), ioaddr + cr );
 
-	return 0;
+	sis_priv->dirty_rx = dirty_rx;
+	sis_priv->cur_rx = cur_rx;
+
+	return count;
 }
 
 /**
@@ -1854,24 +1816,28 @@ refill_rx_ring:
  *	don't do "too much" work here
  */
 
-static void sis900_finish_xmit (struct net_device *net_dev)
+static int sis900_finish_xmit (struct net_device *net_dev)
 {
 	struct sis900_private *sis_priv = net_dev->priv;
+	struct net_device_stats *stats = &sis_priv->stats;
+	int cur_tx = sis_priv->cur_tx;
+	int orig_dirty_tx = sis_priv->dirty_tx;
+	int dirty_tx;
 
-	for (; sis_priv->dirty_tx != sis_priv->cur_tx; sis_priv->dirty_tx++) {
+	for (dirty_tx = orig_dirty_tx; dirty_tx < cur_tx; dirty_tx++) {
 		struct sk_buff *skb;
 		unsigned int entry;
 		u32 tx_status;
 
-		entry = sis_priv->dirty_tx % NUM_TX_DESC;
+		entry = dirty_tx % NUM_TX_DESC;
 		tx_status = sis_priv->tx_ring[entry].cmdsts;
 
-		if (tx_status & OWN) {
-			/* The packet is not transmitted yet (owned by hardware) !
-			 * Note: the interrupt is generated only when Tx Machine
-			 * is idle, so this is an almost impossible case */
+		/* The packet is not transmitted yet (owned by hardware) !
+		 * Note: the interrupt is generated only when Tx Machine
+		 * is idle, so this is an almost impossible case 
+		 */
+		if (tx_status & OWN)
 			break;
-		}
 
 		if (tx_status & (ABORT | UNDERRUN | OWCOLL)) {
 			/* packet unsuccessfully transmitted */
@@ -1879,20 +1845,20 @@ static void sis900_finish_xmit (struct net_device *net_dev)
 				printk(KERN_DEBUG "%s: Transmit "
 				       "error, Tx status %8.8x.\n",
 				       net_dev->name, tx_status);
-			sis_priv->stats.tx_errors++;
+			stats->tx_errors++;
 			if (tx_status & UNDERRUN)
-				sis_priv->stats.tx_fifo_errors++;
+				stats->tx_fifo_errors++;
 			if (tx_status & ABORT)
-				sis_priv->stats.tx_aborted_errors++;
+				stats->tx_aborted_errors++;
 			if (tx_status & NOCARRIER)
-				sis_priv->stats.tx_carrier_errors++;
+				stats->tx_carrier_errors++;
 			if (tx_status & OWCOLL)
-				sis_priv->stats.tx_window_errors++;
+				stats->tx_window_errors++;
 		} else {
 			/* packet successfully transmitted */
-			sis_priv->stats.collisions += (tx_status & COLCNT) >> 16;
-			sis_priv->stats.tx_bytes += tx_status & DSIZE;
-			sis_priv->stats.tx_packets++;
+			stats->collisions += (tx_status & COLCNT) >> 16;
+			stats->tx_bytes += tx_status & DSIZE;
+			stats->tx_packets++;
 		}
 		/* Free the original skb. */
 		skb = sis_priv->tx_skbuff[entry];
@@ -1905,13 +1871,15 @@ static void sis900_finish_xmit (struct net_device *net_dev)
 		sis_priv->tx_ring[entry].cmdsts = 0;
 	}
 
-	if (sis_priv->tx_full && netif_queue_stopped(net_dev) &&
-	    sis_priv->cur_tx - sis_priv->dirty_tx < NUM_TX_DESC - 4) {
-		/* The ring is no longer full, clear tx_full and schedule
-		 * more transmission by netif_wake_queue(net_dev) */
-		sis_priv->tx_full = 0;
+	/* The ring is no longer full, schedule
+	 * more transmission by netif_wake_queue(net_dev) 
+	 */
+	if (netif_queue_stopped(net_dev) && (cur_tx - dirty_tx < NUM_TX_DESC))
 		netif_wake_queue (net_dev);
-	}
+
+	sis_priv->dirty_tx = dirty_tx;
+
+	return dirty_tx - orig_dirty_tx;
 }
 
 /**
@@ -2462,7 +2430,7 @@ static int sis900_resume(struct pci_dev *pci_dev)
 	sis900_set_mode(ioaddr, HW_SPEED_10_MBPS, FDX_CAPABLE_HALF_SELECTED);
 
 	/* Enable all known interrupts by setting the interrupt mask. */
-	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxIDLE), ioaddr + imr);
+	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
 	outl(RxENA | inl(ioaddr + cr), ioaddr + cr);
 	outl(IE, ioaddr + ier);
 
diff --git a/drivers/net/sis900.h b/drivers/net/sis900.h
index 150511a..671af28 100644
--- a/drivers/net/sis900.h
+++ b/drivers/net/sis900.h
@@ -319,8 +319,8 @@ enum sis630_revision_id {
 #define TX_BUF_SIZE     (MAX_FRAME_SIZE+18)
 #define RX_BUF_SIZE     (MAX_FRAME_SIZE+18)
 
-#define NUM_TX_DESC     16      	/* Number of Tx descriptor registers. */
-#define NUM_RX_DESC     16       	/* Number of Rx descriptor registers. */
+#define NUM_TX_DESC     64    	/* Number of Tx descriptor registers. */
+#define NUM_RX_DESC     64    	/* Number of Rx descriptor registers. */
 #define TX_TOTAL_SIZE	NUM_TX_DESC*sizeof(BufferDesc)
 #define RX_TOTAL_SIZE	NUM_RX_DESC*sizeof(BufferDesc)
 

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[jamal]

On Mon, 2007-03-09 at 20:20 -0700, Mandeep Singh Baines wrote:

> I didn't see much saving in interrupts on my machine (too fast, I guess). 

You could try the idea suggested by Dave earlier and just turn interupts
for every nth packet. That should cut down the numbers.

> I did see a significant boost to tx performance by optimizing start_xmit: more
> than double pps in pktgen.

148Kpps on a slow piece of hardware aint bad - Good Stuff. I wonder how
much CPU is being abused.

If you wanna go one extra mile (separate future patch): get rid of that
tx lock and use netif_tx_lock on the interupt path. Look at some sane
driver like tg3 for reference.

cheers,
jamal

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[Daniele Venzano]

----- Message d'origine -----
De: Mandeep Singh Baines <mandeep.baines@gmail.com>
Date: Mon, 3 Sep 2007 20:20:36 -0700
Sujet: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

>Hi Daniele,
>
>Attached is a patch for converting the sis900 driver to NAPI. Please take a
>look at let me know what you think. I'm not 100% sure if I'm handling the
>rotting packet issue correctly or that I have the locking right in tx_timeout.
>These might be areas to look at closely.
>
>I didn't see much saving in interrupts on my machine (too fast, I guess). But
>I still think its beneficial: pushing work out of the interrupt handler into
>a bottom half is a good thing and we no longer need to disable interrupts 
>in start_xmit. 
>
>I did see a significant boost to tx performance by optimizing start_xmit: more
>than double pps in pktgen.
>
>I'm also attaching some test results for various iterations of development.

The patch looks good and I think it can be pushed higher (-mm ?) for some wider 
testing. I don't have the hardware available to do some tests myself, 
unfortunately, but it would be similar to yours anyway.

I'd like to know how this works for people with less memory and slower CPU, but any 
kind of test run will be appreciated.

Thanks, bye.


--
Daniele Venzano
venza@brownhat.org

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[Mandeep Baines]

On 9/4/07, jamal <hadi@cyberus.ca> wrote:
> On Mon, 2007-03-09 at 20:20 -0700, Mandeep Singh Baines wrote:
>
> > I didn't see much saving in interrupts on my machine (too fast, I guess).
>
> You could try the idea suggested by Dave earlier and just turn interupts
> for every nth packet. That should cut down the numbers.
>

I wanted to do that but I couldn't figure out how to free the last skb
if it happened to be a transmit that didn't generate a tx completion
interrupt.

Let's say I interrupt every 4th packet.I've already sent packets 0 to
4. Now I send packets 5 and 6. I can't figure out how to ensure that
the skb's for these packets get freed in a deterministic amount of
time if there is no interrupt? They will get freed when packet 8 gets
transmitted but there is no upper bound on when that will happen.

Maybe I could create a tx skb cleanup timer that I kickoff in
hard_start_xmit(). Every call to hard_start_xmit would reset the
timer. I could try this for a future patch. Not sure if the extra code
would cost me more than I get back in savings.

> > I did see a significant boost to tx performance by optimizing start_xmit: more
> > than double pps in pktgen.
>
> 148Kpps on a slow piece of hardware aint bad - Good Stuff. I wonder how
> much CPU is being abused.
>
> If you wanna go one extra mile (separate future patch): get rid of that
> tx lock and use netif_tx_lock on the interupt path. Look at some sane
> driver like tg3 for reference.
>

Cool. I'll check out the tg3.

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[Mandeep Baines]

Cool. I'll try to see if I can clock my pc lower and run the
experiments again. I'll measure cpu utilization also this time around.
That should be useful for extrapolating.

Regards,
Mandeep

On 9/4/07, Daniele Venzano <venza@brownhat.org> wrote:
> ----- Message d'origine -----
> De: Mandeep Singh Baines <mandeep.baines@gmail.com>
> Date: Mon, 3 Sep 2007 20:20:36 -0700
> Sujet: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition
>
> >Hi Daniele,
> >
> >Attached is a patch for converting the sis900 driver to NAPI. Please take a
> >look at let me know what you think. I'm not 100% sure if I'm handling the
> >rotting packet issue correctly or that I have the locking right in tx_timeout.
> >These might be areas to look at closely.
> >
> >I didn't see much saving in interrupts on my machine (too fast, I guess). But
> >I still think its beneficial: pushing work out of the interrupt handler into
> >a bottom half is a good thing and we no longer need to disable interrupts
> >in start_xmit.
> >
> >I did see a significant boost to tx performance by optimizing start_xmit: more
> >than double pps in pktgen.
> >
> >I'm also attaching some test results for various iterations of development.
>
> The patch looks good and I think it can be pushed higher (-mm ?) for some wider
> testing. I don't have the hardware available to do some tests myself,
> unfortunately, but it would be similar to yours anyway.
>
> I'd like to know how this works for people with less memory and slower CPU, but any
> kind of test run will be appreciated.
>
> Thanks, bye.
>
>
> --
> Daniele Venzano
> venza@brownhat.org
>

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[Mandeep Singh Baines]

[-- Attachment #1: Type: text/plain, Size: 1137 bytes --]

Daniele Venzano (venza@brownhat.org) wrote:
> The patch looks good and I think it can be pushed higher (-mm ?) for some wider 
> testing. I don't have the hardware available to do some tests myself, 
> unfortunately, but it would be similar to yours anyway.
> 
> I'd like to know how this works for people with less memory and slower CPU, but any 
> kind of test run will be appreciated.

Hi Daniele,

I tested the driver under different setting of CPU clock. Under a lower clock,
I get less interrupts (what I was hoping for) and slightly less performance.
Under higher clock, I get better performance and almost 1 interrupt per packet.

I also made a tiny change to the driver which resulted in slightly better
performance and less interrupts. I made a one-line change to finish_xmit,
which now wakes up the transmit queue if there are at least 16 available
slots in the tx ring. Previously, the driver would wake up the transmit queue
if there was just a single slot available. This should result in better
hysteresis.

Attached are my test results and a new patch.

Signed-off-by: Mandeep Singh Baines <mandeep.baines@gmail.com>

--

[-- Attachment #2: sis900_napi_v2.patch --]
[-- Type: text/plain, Size: 19802 bytes --]

diff --git a/drivers/net/sis900.c b/drivers/net/sis900.c
index 7c6e480..40c1aee 100644
--- a/drivers/net/sis900.c
+++ b/drivers/net/sis900.c
@@ -185,7 +185,6 @@ struct sis900_private {
 	dma_addr_t tx_ring_dma;
 	dma_addr_t rx_ring_dma;
 
-	unsigned int tx_full; /* The Tx queue is full. */
 	u8 host_bridge_rev;
 	u8 chipset_rev;
 };
@@ -202,8 +201,10 @@ MODULE_PARM_DESC(max_interrupt_work, "SiS 900/7016 maximum events handled per in
 MODULE_PARM_DESC(sis900_debug, "SiS 900/7016 bitmapped debugging message level");
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-static void sis900_poll(struct net_device *dev);
+static void sis900_poll_controller(struct net_device *dev);
 #endif
+
+static int sis900_poll(struct net_device *dev, int *budget);
 static int sis900_open(struct net_device *net_dev);
 static int sis900_mii_probe (struct net_device * net_dev);
 static void sis900_init_rxfilter (struct net_device * net_dev);
@@ -216,8 +217,8 @@ static void sis900_tx_timeout(struct net_device *net_dev);
 static void sis900_init_tx_ring(struct net_device *net_dev);
 static void sis900_init_rx_ring(struct net_device *net_dev);
 static int sis900_start_xmit(struct sk_buff *skb, struct net_device *net_dev);
-static int sis900_rx(struct net_device *net_dev);
-static void sis900_finish_xmit (struct net_device *net_dev);
+static int sis900_rx(struct net_device *net_dev, int limit);
+static int sis900_finish_xmit (struct net_device *net_dev);
 static irqreturn_t sis900_interrupt(int irq, void *dev_instance);
 static int sis900_close(struct net_device *net_dev);
 static int mii_ioctl(struct net_device *net_dev, struct ifreq *rq, int cmd);
@@ -474,9 +475,11 @@ static int __devinit sis900_probe(struct pci_dev *pci_dev,
 	net_dev->tx_timeout = sis900_tx_timeout;
 	net_dev->watchdog_timeo = TX_TIMEOUT;
 	net_dev->ethtool_ops = &sis900_ethtool_ops;
+	net_dev->poll = &sis900_poll;
+	net_dev->weight = 64;
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-        net_dev->poll_controller = &sis900_poll;
+        net_dev->poll_controller = &sis900_poll_controller;
 #endif
 
 	if (sis900_debug > 0)
@@ -979,13 +982,44 @@ static u16 sis900_reset_phy(struct net_device *net_dev, int phy_addr)
 	return status;
 }
 
+static int sis900_poll(struct net_device *dev, int *budget)
+{
+	struct sis900_private *sis_priv = dev->priv;
+	long ioaddr = dev->base_addr;
+	int limit = min_t(int, dev->quota, *budget);
+	int rx_work_done;
+	int tx_work_done;
+
+	/* run TX completion thread */
+	spin_lock(sis_priv->lock);
+	tx_work_done = sis900_finish_xmit(dev);
+	spin_unlock(sis_priv->lock);
+
+	/* run RX thread */
+	rx_work_done = sis900_rx(dev, limit);
+	*budget -= rx_work_done;
+	dev->quota -= rx_work_done;
+
+	/* re-enable interrupts if no work done */
+	if (rx_work_done + tx_work_done == 0) {
+		netif_rx_complete(dev);
+		/* Enable all known interrupts. */
+		outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
+		/* Handle rotting packet */
+		sis900_rx(dev, NUM_RX_DESC);
+		return 0;
+	}
+
+	return 1;
+}
+
 #ifdef CONFIG_NET_POLL_CONTROLLER
 /*
  * Polling 'interrupt' - used by things like netconsole to send skbs
  * without having to re-enable interrupts. It's not called while
  * the interrupt routine is executing.
 */
-static void sis900_poll(struct net_device *dev)
+static void sis900_poll_controller(struct net_device *dev)
 {
 	disable_irq(dev->irq);
 	sis900_interrupt(dev->irq, dev);
@@ -1032,7 +1066,7 @@ sis900_open(struct net_device *net_dev)
 	sis900_set_mode(ioaddr, HW_SPEED_10_MBPS, FDX_CAPABLE_HALF_SELECTED);
 
 	/* Enable all known interrupts by setting the interrupt mask. */
-	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxIDLE), ioaddr + imr);
+	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
 	outl(RxENA | inl(ioaddr + cr), ioaddr + cr);
 	outl(IE, ioaddr + ier);
 
@@ -1102,7 +1136,6 @@ sis900_init_tx_ring(struct net_device *net_dev)
 	long ioaddr = net_dev->base_addr;
 	int i;
 
-	sis_priv->tx_full = 0;
 	sis_priv->dirty_tx = sis_priv->cur_tx = 0;
 
 	for (i = 0; i < NUM_TX_DESC; i++) {
@@ -1517,7 +1550,6 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 {
 	struct sis900_private *sis_priv = net_dev->priv;
 	long ioaddr = net_dev->base_addr;
-	unsigned long flags;
 	int i;
 
 	if(netif_msg_tx_err(sis_priv))
@@ -1527,8 +1559,8 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 	/* Disable interrupts by clearing the interrupt mask. */
 	outl(0x0000, ioaddr + imr);
 
-	/* use spinlock to prevent interrupt handler accessing buffer ring */
-	spin_lock_irqsave(&sis_priv->lock, flags);
+	/* use spinlock to prevent bh from accessing buffer ring */
+	spin_lock_bh(&sis_priv->lock);
 
 	/* discard unsent packets */
 	sis_priv->dirty_tx = sis_priv->cur_tx = 0;
@@ -1546,10 +1578,9 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 			sis_priv->stats.tx_dropped++;
 		}
 	}
-	sis_priv->tx_full = 0;
 	netif_wake_queue(net_dev);
 
-	spin_unlock_irqrestore(&sis_priv->lock, flags);
+	spin_unlock_bh(&sis_priv->lock);
 
 	net_dev->trans_start = jiffies;
 
@@ -1557,7 +1588,7 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 	outl(sis_priv->tx_ring_dma, ioaddr + txdp);
 
 	/* Enable all known interrupts by setting the interrupt mask. */
-	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxIDLE), ioaddr + imr);
+	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
 	return;
 }
 
@@ -1574,52 +1605,27 @@ static void sis900_tx_timeout(struct net_device *net_dev)
 static int
 sis900_start_xmit(struct sk_buff *skb, struct net_device *net_dev)
 {
-	struct sis900_private *sis_priv = net_dev->priv;
 	long ioaddr = net_dev->base_addr;
-	unsigned int  entry;
-	unsigned long flags;
-	unsigned int  index_cur_tx, index_dirty_tx;
-	unsigned int  count_dirty_tx;
+	struct sis900_private *sis_priv = net_dev->priv;
+        unsigned int entry;
 
-	/* Don't transmit data before the complete of auto-negotiation */
-	if(!sis_priv->autong_complete){
+	/* Don't transmit data before auto-negotiation is complete */
+	if(unlikely(!sis_priv->autong_complete)){
 		netif_stop_queue(net_dev);
 		return 1;
 	}
 
-	spin_lock_irqsave(&sis_priv->lock, flags);
-
-	/* Calculate the next Tx descriptor entry. */
-	entry = sis_priv->cur_tx % NUM_TX_DESC;
+	/* Set the Tx descriptor and enable Transmit State Machine */
+        entry = sis_priv->cur_tx++ % NUM_TX_DESC;
 	sis_priv->tx_skbuff[entry] = skb;
-
-	/* set the transmit buffer descriptor and enable Transmit State Machine */
 	sis_priv->tx_ring[entry].bufptr = pci_map_single(sis_priv->pci_dev,
 		skb->data, skb->len, PCI_DMA_TODEVICE);
 	sis_priv->tx_ring[entry].cmdsts = (OWN | skb->len);
 	outl(TxENA | inl(ioaddr + cr), ioaddr + cr);
 
-	sis_priv->cur_tx ++;
-	index_cur_tx = sis_priv->cur_tx;
-	index_dirty_tx = sis_priv->dirty_tx;
-
-	for (count_dirty_tx = 0; index_cur_tx != index_dirty_tx; index_dirty_tx++)
-		count_dirty_tx ++;
-
-	if (index_cur_tx == index_dirty_tx) {
-		/* dirty_tx is met in the cycle of cur_tx, buffer full */
-		sis_priv->tx_full = 1;
-		netif_stop_queue(net_dev);
-	} else if (count_dirty_tx < NUM_TX_DESC) {
-		/* Typical path, tell upper layer that more transmission is possible */
-		netif_start_queue(net_dev);
-	} else {
-		/* buffer full, tell upper layer no more transmission */
-		sis_priv->tx_full = 1;
+        /* If Tx ring is full, tell upper layer no more transmission */
+	if (unlikely(sis_priv->cur_tx - sis_priv->dirty_tx >= NUM_TX_DESC))
 		netif_stop_queue(net_dev);
-	}
-
-	spin_unlock_irqrestore(&sis_priv->lock, flags);
 
 	net_dev->trans_start = jiffies;
 
@@ -1650,32 +1656,27 @@ static irqreturn_t sis900_interrupt(int irq, void *dev_instance)
 	u32 status;
 	unsigned int handled = 0;
 
-	spin_lock (&sis_priv->lock);
-
-	do {
-		status = inl(ioaddr + isr);
-
-		if ((status & (HIBERR|TxURN|TxERR|TxIDLE|RxORN|RxERR|RxOK)) == 0)
-			/* nothing intresting happened */
-			break;
+	while ((status = inl(ioaddr + isr))) {
 		handled = 1;
 
-		/* why dow't we break after Tx/Rx case ?? keyword: full-duplex */
-		if (status & (RxORN | RxERR | RxOK))
-			/* Rx interrupt */
-			sis900_rx(net_dev);
+		/* why don't we break after Tx/Rx case ?? 
+		 * keyword: full-duplex 
+		 */
 
-		if (status & (TxURN | TxERR | TxIDLE))
-			/* Tx interrupt */
-			sis900_finish_xmit(net_dev);
+		/* Rx interrupt */
+                if (status & (TxURN|TxERR|TxOK|RxORN|RxERR|RxOK)) {
+			/* Disable all interrupts. */
+			outl(0, ioaddr + imr);
+			netif_rx_schedule(net_dev);
+		}
 
 		/* something strange happened !!! */
-		if (status & HIBERR) {
+		if (status & HIBERR)
 			if(netif_msg_intr(sis_priv))
 				printk(KERN_INFO "%s: Abnormal interrupt,"
-					"status %#8.8x.\n", net_dev->name, status);
-			break;
-		}
+					"status %#8.8x.\n", 
+					net_dev->name, status);
+
 		if (--boguscnt < 0) {
 			if(netif_msg_intr(sis_priv))
 				printk(KERN_INFO "%s: Too much work at interrupt, "
@@ -1683,14 +1684,13 @@ static irqreturn_t sis900_interrupt(int irq, void *dev_instance)
 					net_dev->name, status);
 			break;
 		}
-	} while (1);
+	}
 
 	if(netif_msg_intr(sis_priv))
 		printk(KERN_DEBUG "%s: exiting interrupt, "
 		       "interrupt status = 0x%#8.8x.\n",
 		       net_dev->name, inl(ioaddr + isr));
 
-	spin_unlock (&sis_priv->lock);
 	return IRQ_RETVAL(handled);
 }
 
@@ -1704,25 +1704,29 @@ static irqreturn_t sis900_interrupt(int irq, void *dev_instance)
  *	don't do "too much" work here
  */
 
-static int sis900_rx(struct net_device *net_dev)
+static int sis900_rx(struct net_device *net_dev, int limit)
 {
 	struct sis900_private *sis_priv = net_dev->priv;
+	struct net_device_stats *stats = &sis_priv->stats;
 	long ioaddr = net_dev->base_addr;
-	unsigned int entry = sis_priv->cur_rx % NUM_RX_DESC;
-	u32 rx_status = sis_priv->rx_ring[entry].cmdsts;
-	int rx_work_limit;
+	int cur_rx = sis_priv->cur_rx;
+	int dirty_rx, orig_dirty_rx = sis_priv->dirty_rx;
+	int count;
 
 	if (netif_msg_rx_status(sis_priv))
-		printk(KERN_DEBUG "sis900_rx, cur_rx:%4.4d, dirty_rx:%4.4d "
-		       "status:0x%8.8x\n",
-		       sis_priv->cur_rx, sis_priv->dirty_rx, rx_status);
-	rx_work_limit = sis_priv->dirty_rx + NUM_RX_DESC - sis_priv->cur_rx;
+		printk(KERN_DEBUG "sis900_rx, cur_rx:%4.4d, dirty_rx:%4.4d\n",
+		       cur_rx, orig_dirty_rx);
 
-	while (rx_status & OWN) {
+	for (count = 0; count < limit; cur_rx++, count++) {
+		unsigned int entry;
+		u32 rx_status;
 		unsigned int rx_size;
 		unsigned int data_size;
 
-		if (--rx_work_limit < 0)
+		entry = cur_rx % NUM_RX_DESC;
+		rx_status = sis_priv->rx_ring[entry].cmdsts;
+
+		if ((rx_status & OWN) == 0)
 			break;
 
 		data_size = rx_status & DSIZE;
@@ -1735,113 +1739,71 @@ static int sis900_rx(struct net_device *net_dev)
 #endif
 
 		if (rx_status & (ABORT|OVERRUN|TOOLONG|RUNT|RXISERR|CRCERR|FAERR)) {
-			/* corrupted packet received */
-			if (netif_msg_rx_err(sis_priv))
-				printk(KERN_DEBUG "%s: Corrupted packet "
-				       "received, buffer status = 0x%8.8x/%d.\n",
-				       net_dev->name, rx_status, data_size);
-			sis_priv->stats.rx_errors++;
+			pci_unmap_single(sis_priv->pci_dev,
+				sis_priv->rx_ring[entry].bufptr, RX_BUF_SIZE,
+				PCI_DMA_FROMDEVICE);
+			dev_kfree_skb(sis_priv->rx_skbuff[entry]);
+
+			stats->rx_errors++;
 			if (rx_status & OVERRUN)
-				sis_priv->stats.rx_over_errors++;
+				stats->rx_over_errors++;
 			if (rx_status & (TOOLONG|RUNT))
-				sis_priv->stats.rx_length_errors++;
+				stats->rx_length_errors++;
 			if (rx_status & (RXISERR | FAERR))
-				sis_priv->stats.rx_frame_errors++;
+				stats->rx_frame_errors++;
 			if (rx_status & CRCERR)
-				sis_priv->stats.rx_crc_errors++;
-			/* reset buffer descriptor state */
-			sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
+				stats->rx_crc_errors++;
 		} else {
 			struct sk_buff * skb;
-			struct sk_buff * rx_skb;
 
 			pci_unmap_single(sis_priv->pci_dev,
 				sis_priv->rx_ring[entry].bufptr, RX_BUF_SIZE,
 				PCI_DMA_FROMDEVICE);
 
-			/* refill the Rx buffer, what if there is not enought
-			 * memory for new socket buffer ?? */
-			if ((skb = dev_alloc_skb(RX_BUF_SIZE)) == NULL) {
-				/*
-				 * Not enough memory to refill the buffer
-				 * so we need to recycle the old one so
-				 * as to avoid creating a memory hole
-				 * in the rx ring
-				 */
-				skb = sis_priv->rx_skbuff[entry];
-				sis_priv->stats.rx_dropped++;
-				goto refill_rx_ring;
-			}	
-
-			/* This situation should never happen, but due to
-			   some unknow bugs, it is possible that
-			   we are working on NULL sk_buff :-( */
-			if (sis_priv->rx_skbuff[entry] == NULL) {
-				if (netif_msg_rx_err(sis_priv))
-					printk(KERN_WARNING "%s: NULL pointer "
-					      "encountered in Rx ring\n"
-					      "cur_rx:%4.4d, dirty_rx:%4.4d\n",
-					      net_dev->name, sis_priv->cur_rx,
-					      sis_priv->dirty_rx);
-				break;
-			}
-
 			/* give the socket buffer to upper layers */
-			rx_skb = sis_priv->rx_skbuff[entry];
-			skb_put(rx_skb, rx_size);
-			rx_skb->protocol = eth_type_trans(rx_skb, net_dev);
-			netif_rx(rx_skb);
+			skb = sis_priv->rx_skbuff[entry];
+			skb_put(skb, rx_size);
+			skb->protocol = eth_type_trans(skb, net_dev);
+			netif_receive_skb(skb);
 
 			/* some network statistics */
 			if ((rx_status & BCAST) == MCAST)
-				sis_priv->stats.multicast++;
+				stats->multicast++;
 			net_dev->last_rx = jiffies;
-			sis_priv->stats.rx_bytes += rx_size;
-			sis_priv->stats.rx_packets++;
-			sis_priv->dirty_rx++;
-refill_rx_ring:
-			sis_priv->rx_skbuff[entry] = skb;
-			sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
-                	sis_priv->rx_ring[entry].bufptr =
-				pci_map_single(sis_priv->pci_dev, skb->data,
-					RX_BUF_SIZE, PCI_DMA_FROMDEVICE);
+			stats->rx_bytes += rx_size;
+			stats->rx_packets++;
 		}
-		sis_priv->cur_rx++;
-		entry = sis_priv->cur_rx % NUM_RX_DESC;
-		rx_status = sis_priv->rx_ring[entry].cmdsts;
-	} // while
+	}
 
-	/* refill the Rx buffer, what if the rate of refilling is slower
-	 * than consuming ?? */
-	for (; sis_priv->cur_rx != sis_priv->dirty_rx; sis_priv->dirty_rx++) {
+	/* refill the Rx ring. */
+	for (dirty_rx = orig_dirty_rx; dirty_rx < cur_rx; dirty_rx++) {
 		struct sk_buff *skb;
+		unsigned int entry;
 
-		entry = sis_priv->dirty_rx % NUM_RX_DESC;
-
-		if (sis_priv->rx_skbuff[entry] == NULL) {
-			if ((skb = dev_alloc_skb(RX_BUF_SIZE)) == NULL) {
-				/* not enough memory for skbuff, this makes a
-				 * "hole" on the buffer ring, it is not clear
-				 * how the hardware will react to this kind
-				 * of degenerated buffer */
-				if (netif_msg_rx_err(sis_priv))
-					printk(KERN_INFO "%s: Memory squeeze,"
-						"deferring packet.\n",
-						net_dev->name);
-				sis_priv->stats.rx_dropped++;
-				break;
-			}
-			sis_priv->rx_skbuff[entry] = skb;
-			sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
-                	sis_priv->rx_ring[entry].bufptr =
-				pci_map_single(sis_priv->pci_dev, skb->data,
-					RX_BUF_SIZE, PCI_DMA_FROMDEVICE);
+		if ((skb = dev_alloc_skb(RX_BUF_SIZE)) == NULL) {
+			if (netif_msg_rx_err(sis_priv))
+				printk(KERN_INFO "%s: Memory squeeze,"
+					"deferring packet.\n",
+					net_dev->name);
+			break;
 		}
+
+		entry = dirty_rx % NUM_RX_DESC;
+		sis_priv->rx_skbuff[entry] = skb;
+		sis_priv->rx_ring[entry].cmdsts = RX_BUF_SIZE;
+               	sis_priv->rx_ring[entry].bufptr =
+			pci_map_single(sis_priv->pci_dev, skb->data,
+				RX_BUF_SIZE, PCI_DMA_FROMDEVICE);
 	}
+
 	/* re-enable the potentially idle receive state matchine */
-	outl(RxENA | inl(ioaddr + cr), ioaddr + cr );
+	if (dirty_rx != orig_dirty_rx)
+		outl(RxENA | inl(ioaddr + cr), ioaddr + cr );
 
-	return 0;
+	sis_priv->dirty_rx = dirty_rx;
+	sis_priv->cur_rx = cur_rx;
+
+	return count;
 }
 
 /**
@@ -1854,24 +1816,28 @@ refill_rx_ring:
  *	don't do "too much" work here
  */
 
-static void sis900_finish_xmit (struct net_device *net_dev)
+static int sis900_finish_xmit (struct net_device *net_dev)
 {
 	struct sis900_private *sis_priv = net_dev->priv;
+	struct net_device_stats *stats = &sis_priv->stats;
+	int cur_tx = sis_priv->cur_tx;
+	int orig_dirty_tx = sis_priv->dirty_tx;
+	int dirty_tx;
 
-	for (; sis_priv->dirty_tx != sis_priv->cur_tx; sis_priv->dirty_tx++) {
+	for (dirty_tx = orig_dirty_tx; dirty_tx < cur_tx; dirty_tx++) {
 		struct sk_buff *skb;
 		unsigned int entry;
 		u32 tx_status;
 
-		entry = sis_priv->dirty_tx % NUM_TX_DESC;
+		entry = dirty_tx % NUM_TX_DESC;
 		tx_status = sis_priv->tx_ring[entry].cmdsts;
 
-		if (tx_status & OWN) {
-			/* The packet is not transmitted yet (owned by hardware) !
-			 * Note: the interrupt is generated only when Tx Machine
-			 * is idle, so this is an almost impossible case */
+		/* The packet is not transmitted yet (owned by hardware) !
+		 * Note: the interrupt is generated only when Tx Machine
+		 * is idle, so this is an almost impossible case 
+		 */
+		if (tx_status & OWN)
 			break;
-		}
 
 		if (tx_status & (ABORT | UNDERRUN | OWCOLL)) {
 			/* packet unsuccessfully transmitted */
@@ -1879,20 +1845,20 @@ static void sis900_finish_xmit (struct net_device *net_dev)
 				printk(KERN_DEBUG "%s: Transmit "
 				       "error, Tx status %8.8x.\n",
 				       net_dev->name, tx_status);
-			sis_priv->stats.tx_errors++;
+			stats->tx_errors++;
 			if (tx_status & UNDERRUN)
-				sis_priv->stats.tx_fifo_errors++;
+				stats->tx_fifo_errors++;
 			if (tx_status & ABORT)
-				sis_priv->stats.tx_aborted_errors++;
+				stats->tx_aborted_errors++;
 			if (tx_status & NOCARRIER)
-				sis_priv->stats.tx_carrier_errors++;
+				stats->tx_carrier_errors++;
 			if (tx_status & OWCOLL)
-				sis_priv->stats.tx_window_errors++;
+				stats->tx_window_errors++;
 		} else {
 			/* packet successfully transmitted */
-			sis_priv->stats.collisions += (tx_status & COLCNT) >> 16;
-			sis_priv->stats.tx_bytes += tx_status & DSIZE;
-			sis_priv->stats.tx_packets++;
+			stats->collisions += (tx_status & COLCNT) >> 16;
+			stats->tx_bytes += tx_status & DSIZE;
+			stats->tx_packets++;
 		}
 		/* Free the original skb. */
 		skb = sis_priv->tx_skbuff[entry];
@@ -1905,13 +1871,16 @@ static void sis900_finish_xmit (struct net_device *net_dev)
 		sis_priv->tx_ring[entry].cmdsts = 0;
 	}
 
-	if (sis_priv->tx_full && netif_queue_stopped(net_dev) &&
-	    sis_priv->cur_tx - sis_priv->dirty_tx < NUM_TX_DESC - 4) {
-		/* The ring is no longer full, clear tx_full and schedule
-		 * more transmission by netif_wake_queue(net_dev) */
-		sis_priv->tx_full = 0;
+	/* The ring is no longer full, schedule
+	 * more transmission by netif_wake_queue(net_dev) 
+	 */
+	if (netif_queue_stopped(net_dev) && 
+	    (cur_tx - dirty_tx < NUM_TX_DESC - 16))
 		netif_wake_queue (net_dev);
-	}
+
+	sis_priv->dirty_tx = dirty_tx;
+
+	return dirty_tx - orig_dirty_tx;
 }
 
 /**
@@ -2462,7 +2431,7 @@ static int sis900_resume(struct pci_dev *pci_dev)
 	sis900_set_mode(ioaddr, HW_SPEED_10_MBPS, FDX_CAPABLE_HALF_SELECTED);
 
 	/* Enable all known interrupts by setting the interrupt mask. */
-	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxIDLE), ioaddr + imr);
+	outl((RxSOVR|RxORN|RxERR|RxOK|TxURN|TxERR|TxOK), ioaddr + imr);
 	outl(RxENA | inl(ioaddr + cr), ioaddr + cr);
 	outl(IE, ioaddr + ier);
 
diff --git a/drivers/net/sis900.h b/drivers/net/sis900.h
index 150511a..671af28 100644
--- a/drivers/net/sis900.h
+++ b/drivers/net/sis900.h
@@ -319,8 +319,8 @@ enum sis630_revision_id {
 #define TX_BUF_SIZE     (MAX_FRAME_SIZE+18)
 #define RX_BUF_SIZE     (MAX_FRAME_SIZE+18)
 
-#define NUM_TX_DESC     16      	/* Number of Tx descriptor registers. */
-#define NUM_RX_DESC     16       	/* Number of Rx descriptor registers. */
+#define NUM_TX_DESC     64    	/* Number of Tx descriptor registers. */
+#define NUM_RX_DESC     64    	/* Number of Rx descriptor registers. */
 #define TX_TOTAL_SIZE	NUM_TX_DESC*sizeof(BufferDesc)
 #define RX_TOTAL_SIZE	NUM_RX_DESC*sizeof(BufferDesc)
 

[-- Attachment #3: sis900_testingv2.txt --]
[-- Type: text/plain, Size: 2025 bytes --]

Tested using pktgen.

All test were run on the same H/W. The CPU clock was changed from the BIOS
and the machine rebooted before each iteration.

Results in pps. Sending 4000000 60-byte packets.

Iteration 0 (under-clocked 1052.476 MHz):
Cpu(s):  0.3%us, 13.6%sy,  0.0%ni,  0.0%id,  0.0%wa, 31.2%hi, 54.8%si,  0.0%st
Result: OK: 28910148(c28791584+d118564) usec, 4000000 (60byte,0frags)
  138359pps 66Mb/sec (66412320bps) errors: 0
Interrupts: 3234740

Iteration 1 (normal 1397.657 MHz):
Cpu(s):  0.3%us, 20.9%sy,  0.0%ni,  0.0%id,  0.0%wa, 29.9%hi, 48.8%si,  0.0%st
Result: OK: 26947273(c22637342+d4309931) usec, 4000000 (60byte,0frags)
  148438pps 71Mb/sec (71250240bps) errors: 0
Interrupts: 3998176

Iteration 2 (over-clocked 1575.819 MHz):
Cpu(s):  0.3%us, 33.0%sy,  0.0%ni,  0.0%id,  0.0%wa, 27.3%hi, 39.3%si,  0.0%st
Result: OK: 26937148(c21656005+d5281143) usec, 4000000 (60byte,0frags)
  148493pps 71Mb/sec (71276640bps) errors: 0
Interrupts: 3999634

The next few iterations are with a change to the driver. Modified finish_xmit
to only wake the transmit queue when there are least 16 free spots in the tx
ring. Previously, the driver would wake the transmit queue when there was at
least 1 free spot in the tx ring. This should add some hysteresis.

Iteration 3 (under-clocked 1052.476 MHz):
Cpu(s):  0.3%us, 16.3%sy,  0.0%ni,  0.0%id,  0.0%wa, 30.0%hi, 53.3%si,  0.0%st
Result: OK: 28246751(c28169436+d77315) usec, 4000000 (60byte,0frags)
  141609pps 67Mb/sec (67972320bps) errors: 0
Interrupts: 3227925

Iteration 4 (normal 1397.657 MHz):
Cpu(s):  0.3%us, 23.7%sy,  0.0%ni,  0.0%id,  0.0%wa, 30.0%hi, 46.0%si,  0.0%st
Result: OK: 26935554(c25058872+d1876682) usec, 4000000 (60byte,0frags)
  148502pps 71Mb/sec (71280960bps) errors: 0
Interrupts: 3994491

Iteration 5 (over-clocked 1575.819 MHz):
Cpu(s):  0.3%us, 30.8%sy,  0.0%ni,  0.0%id,  0.0%wa, 27.2%hi, 41.7%si,  0.0%st
Result: OK: 26933751(c23148154+d3785597) usec, 4000000 (60byte,0frags)
  148512pps 71Mb/sec (71285760bps) errors: 0
Interrupts: 3999595

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[James Chapman]

Mandeep Singh Baines wrote:
> Daniele Venzano (venza@brownhat.org) wrote:
>> The patch looks good and I think it can be pushed higher (-mm ?) for some wider 
>> testing. I don't have the hardware available to do some tests myself, 
>> unfortunately, but it would be similar to yours anyway.
>>
>> I'd like to know how this works for people with less memory and slower CPU, but any 
>> kind of test run will be appreciated.
> 
> Hi Daniele,
> 
> I tested the driver under different setting of CPU clock. Under a lower clock,
> I get less interrupts (what I was hoping for) and slightly less performance.
> Under higher clock, I get better performance and almost 1 interrupt per packet.

I have a patch that solves the high interrupt rate problem by keeping 
the driver in polled mode longer. It's written for the latest NAPI 
version that DaveM posted recently. I'll try to get some time to write 
it up and post it for comment.

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[jamal]

On Wed, 2007-05-09 at 13:03 +0100, James Chapman wrote:

> I have a patch that solves the high interrupt rate problem by keeping 
> the driver in polled mode longer. It's written for the latest NAPI 
> version that DaveM posted recently. I'll try to get some time to write 
> it up and post it for comment.

Theres interesting challenges to be tackled with resolving that. 
Just so you dont reinvent the wheel or to help invent a better one;
please read:
http://kernel.org/pub/linux/kernel/people/hadi/docs/UKUUG2005.pdf

if you have, what are the differences in your approach - and when
do you find it useful?

cheers,
jamal

PS:- Mandeep, i was going to suggest thresholds but you beat me to it
with your latest patch.

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[James Chapman]

jamal wrote:
> On Wed, 2007-05-09 at 13:03 +0100, James Chapman wrote:
> 
>> I have a patch that solves the high interrupt rate problem by keeping 
>> the driver in polled mode longer. It's written for the latest NAPI 
>> version that DaveM posted recently. I'll try to get some time to write 
>> it up and post it for comment.
> 
> Theres interesting challenges to be tackled with resolving that. 
> Just so you dont reinvent the wheel or to help invent a better one;
> please read:
> http://kernel.org/pub/linux/kernel/people/hadi/docs/UKUUG2005.pdf
> 
> if you have, what are the differences in your approach - and when
> do you find it useful?

Thanks Jamal. Yes, I'd already read your paper. I think my idea is 
different to the ideas described in your paper and I'm in the process of 
writing it up as an RFC to post to netdev. Briefly though, the driver's 
->poll() holds off doing netif_rx_complete() for 1-2 jiffies and keeps 
itself in poll_on mode for that time, consuming no quota. The net_rx 
softirq processing loop is modified to detect the case when the only 
devices in its poll list are doing no work (consuming no quota). The 
driver's ->poll() samples jiffies while it is considering when to do the 
netif_rx_complete() like your Parked state - no timers are used.

If I missed that this approach has already been tried before and 
rejected, please let me know. I see better throughput and latency in my 
packet forwarding and LAN setups using it.

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[jamal]

On Wed, 2007-05-09 at 14:55 +0100, James Chapman wrote:

> Thanks Jamal. Yes, I'd already read your paper. I think my idea is 
> different to the ideas described in your paper 

I am hoping you can pick from the lessons of what has been tried and
failed and the justification for critiqueing something as "Failed". 
If you have - i feel i accomplished something useful writting the paper.

> and I'm in the process of 
> writing it up as an RFC to post to netdev. 

Please cc me if you want my feedback - I am backlogged by about 3000
messages on netdev.

> Briefly though, the driver's 
> ->poll() holds off doing netif_rx_complete() for 1-2 jiffies and keeps 
> itself in poll_on mode for that time, consuming no quota. 
> The net_rx 
> softirq processing loop is modified to detect the case when the only 
> devices in its poll list are doing no work (consuming no quota). The 
> driver's ->poll() samples jiffies while it is considering when to do the 
> netif_rx_complete() like your Parked state - no timers are used.

Ok, so the difference seems to be you actually poll instead for those
jiffies instead starting a timer in the parked state - is that right?

> If I missed that this approach has already been tried before and 
> rejected, please let me know. I see better throughput and latency in my 
> packet forwarding and LAN setups using it.

If you read the paper: There are no issues with high throughput - NAPI
kicks in.
The challenge to be overcome is at low traffic, if you have a real fast
processor your cpu-cycles-used/bits-processed ratio is high....
If you are polling (softirqs have high prio and depending on the cpu,
there could be a few gazillion within those 1-2 jiffies), then isnt the
end result still a high cpu-cycles used?
Thats what the timer tries to avoid (do nothing until some deffered
point).
If you waste cpu cycles and poll, I can see that (to emphasize: For
FastCPU-LowTraffic scenario), you will end up _not_ having latency
issues i pointed out, but you surely have digressed from the original
goal which is to address the cpu abuse at low traffic (because you abuse
more cpu).

One thing that may be valuable is to show that the timers and polls are
not much different in terms of cpu abuse (It's theoretically not true,
but reality may not match).
The other thing is now hrestimers are on, can you try using a piece of
hardware that can get those kicked and see if you see any useful results
on latency.

cheers,
jamal

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[Mandeep Singh Baines]

jamal (hadi@cyberus.ca) wrote:
> On Wed, 2007-05-09 at 14:55 +0100, James Chapman wrote:
> 
> > Thanks Jamal. Yes, I'd already read your paper. I think my idea is 
> > different to the ideas described in your paper 
> 
> I am hoping you can pick from the lessons of what has been tried and
> failed and the justification for critiqueing something as "Failed". 
> If you have - i feel i accomplished something useful writting the paper.
> 
> > and I'm in the process of 
> > writing it up as an RFC to post to netdev. 
> 
> Please cc me if you want my feedback - I am backlogged by about 3000
> messages on netdev.
> 
> > Briefly though, the driver's 
> > ->poll() holds off doing netif_rx_complete() for 1-2 jiffies and keeps 
> > itself in poll_on mode for that time, consuming no quota. 
> > The net_rx 
> > softirq processing loop is modified to detect the case when the only 
> > devices in its poll list are doing no work (consuming no quota). The 
> > driver's ->poll() samples jiffies while it is considering when to do the 
> > netif_rx_complete() like your Parked state - no timers are used.
> 
> Ok, so the difference seems to be you actually poll instead for those
> jiffies instead starting a timer in the parked state - is that right?
> 
> > If I missed that this approach has already been tried before and 
> > rejected, please let me know. I see better throughput and latency in my 
> > packet forwarding and LAN setups using it.
> 
> If you read the paper: There are no issues with high throughput - NAPI
> kicks in.
> The challenge to be overcome is at low traffic, if you have a real fast
> processor your cpu-cycles-used/bits-processed ratio is high....

I'm not sure cpu-cycles-used/bits-processed is the correct metric to use.
An alternative would be to look at cpu-cycles-used/unit-time (i.e.
CPU utilization or load) for a given bit-rate or packet-rate. This would
make an interesting graph.

At low packet-rate, CPU utilization is low so doing extra work per packet
is probably OK. Utilizing 2% of CPU vesus 1% is negligible. But at higher
rate, when there is more CPU utilization, using 40% of CPU versus 60% is
significant. I think the absolute different in CPU utilization is more
important than the relative difference. iow, 2% versus 1%, even though 
a 2x difference in cpu-cycles/packet, is negligible compared to 40% 
versus 60%.

> If you are polling (softirqs have high prio and depending on the cpu,
> there could be a few gazillion within those 1-2 jiffies), then isnt the
> end result still a high cpu-cycles used?
> Thats what the timer tries to avoid (do nothing until some deffered
> point).

Using a timer might also behave better in a tick-less (CONFIG_NO_HZ) 
configuration.

> If you waste cpu cycles and poll, I can see that (to emphasize: For
> FastCPU-LowTraffic scenario), you will end up _not_ having latency
> issues i pointed out, but you surely have digressed from the original
> goal which is to address the cpu abuse at low traffic (because you abuse
> more cpu).
> 
> One thing that may be valuable is to show that the timers and polls are
> not much different in terms of cpu abuse (It's theoretically not true,
> but reality may not match).
> The other thing is now hrestimers are on, can you try using a piece of
> hardware that can get those kicked and see if you see any useful results
> on latency.
> 
> cheers,
> jamal
> 

Re: [PATCH] [sis900] convert to NAPI, WAS Re: pktgen terminating condition

[jamal]

On Wed, 2007-05-09 at 22:06 -0700, Mandeep Singh Baines wrote:
> jamal (hadi@cyberus.ca) wrote:

> > If you read the paper: There are no issues with high throughput - NAPI
> > kicks in.
> > The challenge to be overcome is at low traffic, if you have a real fast
> > processor your cpu-cycles-used/bits-processed ratio is high....
> 
> I'm not sure cpu-cycles-used/bits-processed is the correct metric to use.
> An alternative would be to look at cpu-cycles-used/unit-time (i.e.
> CPU utilization or load) for a given bit-rate or packet-rate. 

I wasnt explicit but we are saying the same thing. The paper is more
specific: if you make the packet count used constant - this translates
to a unit of time given low traffic rate. If you fix the time,
cpu-cycles are easier to extrapolate from.

> This would make an interesting graph.

If you are to plot a cpu-util vs packet rate, on most modern hardware you will 
see a spike before you hit the MLFRR and then utilization will go down and slowly 
start going up.

> At low packet-rate, CPU utilization is low so doing extra work per packet
> is probably OK. 

Thats the arguement weve used in the past ;-> Unfortunately, with the
relative cost of IO going up you cant keep making that arguement (at
least thats the position presented in the paper). 
Your mileage may vary. If you are running a machine dishing out bulk
transfers probably not a big deal. If you are doing database
transactions, you loose in benchmarks etc.

> Utilizing 2% of CPU vesus 1% is negligible. But at higher
> rate, when there is more CPU utilization, using 40% of CPU versus 60% is
> significant. I think the absolute different in CPU utilization is more
> important than the relative difference. iow, 2% versus 1%, even though 
> a 2x difference in cpu-cycles/packet, is negligible compared to 40% 
> versus 60%.

Refer to above.

> Using a timer might also behave better in a tick-less (CONFIG_NO_HZ) 
> configuration.

good point.

cheers,
jamal