[Question] SMP for TCP/IP Stack

[Question] SMP for TCP/IP Stack

[Hyochang Nam]

Can Linux Kernel 2.4.X handle two IP Packets at the same time
in a SMP machine which has two CPUs?
I have a SMP machine which equips two Intel Xeon CPUs and two
Intel Gigabit Network Cards. When I sent small IP Packets
to the machine, most of packets are dropped. When I watch 
CPU utlization with TOP program, only one CPU shows high value
but the other shows much low value, ie. 10% CPU utlization.
My test shows current IP Stack in Linux Kernel cannot provide 
SMP Processing properly. But, some articles said Linux Kernel 2.4
gives true SMP processing. What do you think my problem is?

Best regards,

Hyochang Nam

Re: [Question] SMP for TCP/IP Stack

[Benjamin LaHaise]

Have you made sure each nic is on a separate interrrupt and that those 
interrupts are bound to different cpus?

		-ben

On Wed, Sep 25, 2002 at 11:27:31AM +0900, Hyochang Nam wrote:
> 
> Can Linux Kernel 2.4.X handle two IP Packets at the same time
> in a SMP machine which has two CPUs?
> I have a SMP machine which equips two Intel Xeon CPUs and two
> Intel Gigabit Network Cards. When I sent small IP Packets
> to the machine, most of packets are dropped. When I watch 
> CPU utlization with TOP program, only one CPU shows high value
> but the other shows much low value, ie. 10% CPU utlization.
> My test shows current IP Stack in Linux Kernel cannot provide 
> SMP Processing properly. But, some articles said Linux Kernel 2.4
> gives true SMP processing. What do you think my problem is?
> 
> Best regards,
> 
> Hyochang Nam
> 

-- 
GMS rules.

Re: [Question] SMP for TCP/IP Stack

[Ben Greear]

Hyochang Nam wrote:
> Can Linux Kernel 2.4.X handle two IP Packets at the same time
> in a SMP machine which has two CPUs?
> I have a SMP machine which equips two Intel Xeon CPUs and two
> Intel Gigabit Network Cards. When I sent small IP Packets
> to the machine, most of packets are dropped. When I watch 
> CPU utlization with TOP program, only one CPU shows high value
> but the other shows much low value, ie. 10% CPU utlization.
> My test shows current IP Stack in Linux Kernel cannot provide 
> SMP Processing properly. But, some articles said Linux Kernel 2.4
> gives true SMP processing. What do you think my problem is?
> 
> Best regards,
> 
> Hyochang Nam
> 

I will be interested to hear if your tests can generate heavy traffic
for more than a few hours...my machine keeps crashing when doing this
kind of test.

How many packets are you trying to send?

Also, try loading the NIC with TxDescriptors=4096 RxDescriptors=1024

Enjoy,
Ben

-- 
Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear

Re: [Question] SMP for TCP/IP Stack

[Nivedita Singhvi]

Hyochang Nam wrote:
> 
> Can Linux Kernel 2.4.X handle two IP Packets at the same time
> in a SMP machine which has two CPUs?

We've done tests on large SMP's without significant problems.

> I have a SMP machine which equips two Intel Xeon CPUs and two
> Intel Gigabit Network Cards. When I sent small IP Packets
> to the machine, most of packets are dropped. When I watch

How small is your small packet? Do you have the same problem
with larger packets? 
Are these drops showing up in ifconfig output? i.e. reported
by the card? In which case I suspect it might be a card issue.
Also, have you configured your card settings?

> CPU utlization with TOP program, only one CPU shows high value
> but the other shows much low value, ie. 10% CPU utlization.

How are you doing your sends? Is your application mostly running
on one CPU? Do you have anything else running on the busy CPU?
What is the interrupt distribution between the two CPU's?

> My test shows current IP Stack in Linux Kernel cannot provide
> SMP Processing properly. But, some articles said Linux Kernel 2.4
> gives true SMP processing. What do you think my problem is?

Could you provide your stats (ifconfig, netstat -s)?

> Hyochang Nam

thanks,
Nivedita