Polling For 100 mbps Connections? (Was Re: Freebsd Theme Song)

Drew Tomlinson drew at mykitchentable.net
Tue Dec 13 06:48:34 PST 2005


Ted Mittelstaedt wrote, On 12/13/2005 12:44 AM:

>  
>
>>-----Original Message-----
>>From: Drew Tomlinson [mailto:drew at mykitchentable.net]
>>Sent: Monday, December 12, 2005 12:30 PM
>>To: Ted Mittelstaedt
>>Cc: Michael Vince; danial_thom at yahoo.com; freebsd-questions at freebsd.org;
>>Kris Kennaway
>>Subject: Polling For 100 mbps Connections? (Was Re: Freebsd Theme Song)
>>
>>
>>On 12/12/2005 8:13 AM Ted Mittelstaedt wrote:
>>
>>    
>>
>>>Michael,
>>>
>>> Fundamentally, here's the problem Danial is claiming exists:
>>>
>>>it takes a certain amount of time to get the packet clocked in
>>>      
>>>
>>>from the network into the ethernet receiver.  This is hardware
>>    
>>
>>>dependent and cannot be changed.
>>>
>>>It takes a certain amount of time to get the packet out of
>>>the hardware in the ethernet card into main ram, this also
>>>hardware dependent and cannot be changed. (unless the device
>>>driver is terribly inefficient, which we will assume it's not)
>>>
>>>Once in main ram, the information in the packet has to go through
>>>a number of code statements.  The more code statements the
>>>longer the information in the packet is sitting around in
>>>the FreeBSD system's memory.
>>>
>>>It then takes a certain amount of time to get the information
>>>out of main memory into the other sending ethernet nic's buffers,
>>>
>>>and it takes time to get it out of the sending nic back to the
>>>wire.
>>>
>>>Danial is claiming the slowness is in the main ram section of
>>>things, not in the ethernet driver code.
>>>
>>>polling makes the ethernet driver more efficient at high data
>>>rates, but it does nothing for the speed of processing within
>>>the TCPIP stack itself.  At low data rates polling is less
>>>efficient than the interrupt method.  And unless the nic driver
>>>is terribly inefficient to start with, the time it adds to the
>>>packet path in the system is minor compared to the time spent
>>>in the TCP/IP stack.
>>>
>>>Ted
>>>
>>>
>>>      
>>>
>>Thanks for the explanation.  So would polling be beneficial or
>>detrimental for a 100 mbps Ethernet card?
>>    
>>
>
>Yes, if you were running 100Mbt's of bandwidth through it.
>  
>

I assume you mean "yes it's beneficial"?  :)

>>Not sure if 100 mbps is
>>considered "high" or "low" speed.  I'm specifically interested in
>>NetGear cards using the dc driver or DLink cards using the rl driver.
>>
>>    
>>
>
>The rl chipset isn't known as a very good chipset. YMMV
>  
>

Yeah, I've heard that a lot.  It was an old card I had lying around and 
it seems to work OK for me.  I'm not using it for anything other that 
connecting to a 802.11b wireless bridge.  Very little traffic.

>Some of the Netgear cards use clone 21143 chipsets which are
>extremely inferior to the real thing.  In particular if your
>Netgear card is using a PNIC chipset it is pretty bad with serious
>performance penalty.  This is documented in Section 4 of the dc manpage.
>  
>

This is disapointing.  I was under the impression that NetGear cards 
were pretty good.  But now I looked closer at dmesg.boot and see I have 
the PNIC chipset you mention.  I'll read the dc man page to see what 
penalties I'm suffering.

>People seem to have good results with polling on the fxp cards.
>  
>

Ah, the built in interface on a HP e60 server I have.  It's an old dog 
used as a file server.  It has been nothing but reliable and is still 
chuggin' along just fine.  I'll enable polling on it and see if there's 
any noticeable improvement in transfer rates.  The machine that 
typically is used for large file transfers to and from the e60  is a 
Windows XP box that has a Nvidia Nforce 4 chipset and whatever 
intergrated ethernet port that comes with that chipset.  Are there any 
known issues with this setup that would invalidate my test?

Thanks again for the info.

Drew

>Ted
>
>  
>


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