readme.txt

基于pxa270的linux下smsc9118的网卡驱动源码

working as fast as it can to receive packets and pass them up to 
the OS. In doing so it will hog CPU time and the OS may drop packets
due to lack of an ability to process them. It has been found that
during these heavy traffic conditions, throughput can be significantly
improved if the driver voluntarily releases the CPU. Yes, this will
cause more packets to be dropped on the wire but a greater number
of packets are spared because the OS has more time to process them.

As of version 1.05 and later, the driver implements a new flow control
detection method that operates like this. If the driver detects an
excessive work load in the period of 100mS, then the driver
assumes there is insufficient flow control in use. Therefor it will 
turn on driver level flow control. Which significantly reduces the 
amount of time the driver holds the CPU, and causes more packets to
be dropped on the wire. So a balancing/tuning, needs to be performed
on each system to get the best performance under these conditions. 
If however the driver detects a tolerable work load in a period of 
100mS then it assumes flow control is being managed well and does 
not attempt to intervene by releasing the CPU. Under these conditions
the driver will naturally release the CPU to the OS, since the system
as a whole is keeping up with traffic.

Now that the background has been discussed, its necessary to talk 
about how the driver implements flow control. The method used is a 
work load model. This is similar but not exactly the same as 
throughput. Work load is the sum of all the packet sizes plus a constant
packet cost for each packet. This provides more balance. For instance
a stream of max size packets will give a large throughput with fewer
packets, while a stream of min size packets will give a low throughput
with many packets. Adding a per packet cost to the work load allows these
two cases to both activate and manage flow control. If work load only 
counted packet sizes then only a stream of max size packets would
activate flow control, while a stream of min size packets would not.

There are five primary parameters responsible for managing flow control.
They can be found in the FLOW_CONTROL_PARAMETERS structure. 
They are
	MaxThroughput, Represents the maximum throughput measured in a 
		100mS period, during an rx TCP_STREAM test.		
	MaxPacketCount, Represents the maximum packet count measured in a 
		100mS period, during an rx TCP_STREAM test.
	PacketCost, Represents the optimal per packet cost
	BurstPeriod, Represents the optimal burst period in 100uS units.
	IntDeas, This is the value for the interrupt deassertion period.
	    It is set to INT_DEAS field of the INT_CFG register.
The driver will call Platform_GetFlowControlParameters to get these

parameters for the specific platform and current configuration.
These parameters must be carefully choosen by the driver writer so
optimal performance can be achieved. Therefor it is necessary to 
describe how the driver uses each parameter.

The first three parameters MaxThroughput, MaxPacketCount, and PacketCost,
are used to calculate the secondary parameter, MaxWorkLoad according
to the following formula.
	MaxWorkLoad=MaxThroughput+(MaxPacketCount*PacketCost);
MaxWorkLoad represents the maximum work load the system can handle during
a 100mS period.
	The driver will use MaxWorkLoad and BurstPeriod to determine 
BurstPeriodMaxWorkLoad, which represents the maximum amount of work the 
system can handle during a single burst period. It is calculated as follows
	BurstPeriodMaxWorkLoad=(MaxWorkLoad*BurstPeriod)/1000;

Every 100mS the driver measures the CurrentWorkLoad by the following 
algorithm.

	At the beginning of a 100mS period
		CurrentWorkLoad=0;
		
	During a 100mS period CurrentWorkLoad is adjusted when a packet
	arrives according to the following formula.
		CurrentWorkLoad+=PacketSize+PacketCost;
		
	At the end of a 100mS period
		if(CurrentWorkLoad>((MaxWorkLoad*(100+ActivationMargin))/100)) 
		{
			if(!FlowControlActive) {
				FlowControlActive=TRUE;
				//Do other flow control initialization
				BurstPeriodCurrentWorkLoad=0;
			}
		}
		if(CurrentWorkLoad<((MaxWorkLoad*(100-DeactivationMargin))/100))
		{
			if(FlowControlActive) {
				FlowControlActive=FALSE;
				//Do other flow control clean up
				Enable Receiver interrupts
			}
		}

During periods where flow control is active, that is 
FlowControlActive==TRUE, the driver will manage flow control by the
following algorithm.

	At the end/beginning of a burst period
		if(BurstPeriodCurrentWorkLoad>BurstPeriodMaxWorkLoad) {
			BurstPeriodCurrentWorkLoad-=BurstPeriodMaxWorkLoad;
		} else {
			BurstPeriodCurrentWorkLoad=0;
		}
		Enable Receiver Interrupts;
		
	When checking if a packet arrives
		if(BurstPeriodCurrentWorkLoad<BurstPeriodMaxWorkLoad) {
			//check for packet normally
			BurstPeriodCurrentWorkLoad+=PacketSize+PacketCost;
		} else {
			//Do not check for packet, but rather
			//  behave as though there is no new packet.
			Disable Receiver interrupts
		}

This algorithm will allow the driver to do a specified amount
of work and then give up the CPU until the next burst period. Doing this
allows the OS to process all the packets that have been sent to it.

So that is generally how the driver manages flow control. For more
detail you can refer to the source code. Now it is necessary to 
describe the exact method for obtaining the optimal flow control 
parameters.

When obtaining the optimal flow control parameters it is important
to note the configuration you are using. Generally there are 8
configurations for each platform. They involve the following options
	DMA or PIO
	16 bit or 32 bit
	118/117/112 or 116/115
Some platforms may only use 16 bit mode. While other platforms may 
have a selectable clock rate. What ever the options are, every combination
should be identifiable, and Platform_GetFlowControlParameters should be
implemented to provide the correct flow control parameters. It is important
to be sure that the carefully selected parameters are applied to the
same configuration used during tuning.

Flow control tuning requires a publically available program called
netperf, and netserver, which are a client/server pair. These are built 
with the same make file and can be found on the web.

Fortunately, as of version 1.10, smsc9118 and cmd9118 supports an automated
tuning mechanism. The process takes about one hour and can be initiated as
follows

AUTOMATED TUNING:

Choose the configuration you want to tune. 
That is choose between
  DMA or PIO,
  16 bit or 32 bit,
  118/117/112 or 116/115,
Make sure there is a direct connection between the target platform
and the host platform. Do not use a hub, or switch. The target
platform is the platform that will run this driver. The host platform
should be a PC easily capable of sending wire speed traffic.

Install the driver on your target platform with your choosen configuration.
	insmod smsc9118d.o 
	ifconfig eth1 192.1.1.118
load servers on target platform
	netserver
	cmd9118 -cSERVER
On host platform, make sure the netperf executable is 
located in the same directory and the cmd9118 executable. While in that
directory run the following.
	cmd9118 -cTUNER -H192.1.1.118
This command, if successful, will begin the one hour tuning process.
At the end you will get a dump of the optimal flow control parameters.
The key parameters needed are
    MaxThroughput
    MaxPacketCount
    PacketCost
    BurstPeriod
    IntDeas
These value must be assigned in Platform_GetFlowControlParameters to
	flowControlParameters->MaxThroughput
	flowControlParameters->MaxPacketCount
	flowControlParameters->PacketCost
	flowControlParameters->BurstPeriod
	flowControlParameters->IntDeas
Make sure the Platform_GetFlowControlParameters checks the current configuration
and will only set those parameters if the current configuration matches the
configuration you tuned with.

Next start over but choose a configuration you haven't already tuned.
   

MANUAL TUNING:
In the off chance that the automated tuning fails to work properly, you may
use the following manual tuning procedure.

STEP 1:
	Select a configuration. That is choose between DMA or PIO, 16 bit or 
	32 bit, 118/117/112 or 116/115.
	Make sure there is a direct connection between the target platform
	and the host platform. Do not use a hub, or switch. The target
	platform is the platform that will run this driver. The host platform
	should be a PC easily capable of sending wire speed traffic.

STEP 2:
	load the driver on the target platform with the following commands
		insmod smsc9118.o max_work_load=0 int_deas=ID
		ifconfig eth1 192.1.1.118
		netserver
	ID will be replated by the number you will be adjusting to obtain the
		best throughput score in STEP 3, initially a goog number to start
		with is 0.

STEP 3:
	On  the host platform run the following command
		netperf -H192.1.1.118 
	Examine the output. The goal is to maximize the number on the 
		Throughput column.
	If you are satisfied with the throughput remember the ID number
		you used and move on to STEP 4.
	If you would like to try improving the throughput
		unload the driver on the target with
			ifconfig eth1 down
			rmmod smsc9118
		goto STEP 2 and use a different value for ID

	
STEP 4:
	unload the driver with 
		ifconfig eth1 down
		rmmod smsc9118
	load driver on the target platform with the following commands
		insmod smsc9118.o max_work_load=0 int_deas=ID
		ifconfig eth1 192.1.1.118
		netserver
	NOTE: the driver will be making traffic measurements. Therefor
		it is important not to insert any steps between 4 and 6.
		
STEP 5:	
	run netperf on the host platform
		netperf -H192.1.1.118
	repeat two more times.
	
STEP 6:
	on target platform run the following
		cmd9118 -cGET_FLOW
	Many variables will be displayed. Two of them are measurements we need.
	You can set the following two parameters as follows.
		MaxThroughput  = RxFlowMeasuredMaxThroughput;
		MaxPacketCount = RxFlowMeasuredMaxPacketCount;
		
STEP 7:
	Unload the driver on target platform with
		ifconfig eth1 down
		rmmod smsc9118
	Apply the parameters obtained in STEP 6 and 2/3 to the appropriate location,
		given the configuration choosen in STEP 1, in
		Platform_GetFlowControlParameters. The parameters for your
		choosen configuration should be set as follows
			MaxThroughput = (RxFlowMeasuredMaxThroughput from step 6);
			MaxPacketCount = (RxFlowMeasuredMaxPacketCount from step 6);
			PacketCost=0; //temporarily set to 0
			BurstPeriod=100; //temporarily set to 100
			IntDeas= (ID from step 2/3).
	recompile driver.
		
STEP 8:
	Again make sure your still using the same configuration you selected
		in STEP 1.
	Load recompiled driver on target platform with the following commands
		insmod smsc9118.o burst_period=BP
		ifconfig eth1 192.1.1.118
	BP will be replaced by the number you will be adjusting to obtain the
		best throughput score in STEP 9, initially a good number to 
		start with is 100.

STEP 9:
	On Host platform run the following command
		netperf -H192.1.1.118 -tUDP_STREAM -l10 -- -m1472
	Examine the output.	The goal is to maximize the lower 
		number on the Throughput column.
	If you are satisfied with the throughput remember the BP number 
		you used and move on to STEP 10.
	If you would like to try improving the throughput
		unload the driver on the target with
			ifconfig eth1 down
			rmmod smsc9118
		goto STEP 8 and use a different value for BP.
		
STEP 10:
	unload the driver on target platform
		ifconfig eth1 192.1.1.118 down
		rmmod smsc9118
	Again make sure your still using the same configuration you selected
		in STEP 1.
	Load the recompiled driver from STEP 7 on target platform with 
		insmod smsc9118.o burst_period=BP packet_cost=PC
		ifconfig eth1 192.1.1.118
	BP will be replaced with the value you settled on in STEP 8/9.
	PC will be replaced by the number you will be adjusting to 
		obtain the best throughput score in STEP 11, typically PC ends 
		up somewhere between 100 and 200.

STEP 11:
	On Host platform run the following command
		netperf -H192.1.1.118 -tUDP_STREAM -l10 -- -m16
	Examine the output. The goal is to maximize the lower
		number on the Throughput column.
	If you are satisfied with the throughput remember the PC number
		you used and move on the STEP 12.
	If you would like to try improving the throughput