Re: Gigabit/SMP performance problem

Avery Fay
2003-01-03T20:19:06Z

Dual Pentium 4 Xeon at 2.4 Ghz. I believe I am using irq load balancing as
shown below (seems to be applied to Red Hat's kernel). Here's
/proc/interrupts:

CPU0 CPU1
0: 179670 182501 IO-APIC-edge timer
1: 386 388 IO-APIC-edge keyboard
2: 0 0 XT-PIC cascade
8: 1 0 IO-APIC-edge rtc
12: 9 9 IO-APIC-edge PS/2 Mouse
14: 1698 1511 IO-APIC-edge ide0
24: 1300174 1298071 IO-APIC-level eth2
25: 1935085 1935625 IO-APIC-level eth3
28: 1162013 1162734 IO-APIC-level eth4
29: 1971246 1967758 IO-APIC-level eth5
48: 2753990 2753821 IO-APIC-level eth0
49: 2047386 2043894 IO-APIC-level eth1
72: 838987 841143 IO-APIC-level eth6
73: 2767885 2768307 IO-APIC-level eth7
NMI: 0 0
LOC: 362009 362008
ERR: 0
MIS: 0

I started traffic at different times on the various interfaces so the
number of interrupts per interface aren't uniform.

I modified RxIntDelay, TxIntDelay, RxAbsIntDelay, TxAbsIntDelay,
FlowControl, RxDescriptors, TxDescriptors. Increasing the various
IntDelays seemed to improve performance slightly.

I'm using 3 Intel PRO/1000 MT Dual Port Server adapters as well as 2
onboard Intel PRO/1000 ports. The adapters use the 82546EB chips. I
believe that the onboard ports use the same although I'm not sure.

Should I get rid of IRQ load balancing? And what do you mean "Intel broke the P4's interrupt routing"?

Thanks,
Avery Fay

"Martin J. Bligh" <mbligh@aracnet.com>
01/03/2003 01:05 PM

To: Avery Fay <avery_fay@symantec.com>, linux-kernel@vger.kernel.org
cc:
Subject: Re: Gigabit/SMP performance problem

> I'm working with a dual xeon platform with 4 dual e1000 cards on
different
> pci-x buses. I'm having trouble getting better performance with the
second
> cpu enabled (ht disabled). With a UP kernel (redhat's 2.4.18), I can
route
> about 2.9 gigabits/s at around 90% cpu utilization. With a SMP kernel
> (redhat's 2.4.18), I can route about 2.8 gigabits/s with both cpus at
> around 90% utilization. This suggests to me that the network code is
> serialized. I would expect one of two things from my understanding of
the
> 2.4.x networking improvements (softirqs allowing execution on more than
> one cpu):
>
> 1.) with smp I would get ~2.9 gb/s but the combined cpu utilization
would
> be that of one cpu at 90%.
> 2.) or with smp I would get more than ~2.9 gb/s.
>
> Has anyone been able to utilize more than one cpu with pure forwarding?
>
> Note: I realize that I am not using a stock kernel. I was in the past,
but
> I ran into the same problem (smp not improving performance), just at
lower
> speeds (redhat's kernel was faster). Therefore, this problem is neither
> introduced nor solved by redhat's kernel. If anyone has suggestions for
> improvements, I can move back to a stock kernel.
>
> Note #2: I've tried tweaking a lot of different things including binding

> irq's to specific cpus, playing around with e1000 modules settings, etc.
>
> Thanks in advance and please CC me with any suggestions as I'm not
> subscribed to the list.

Dual what Xeon? I presume a P4 thing. Can you cat /proc/interrupts?
Are you using the irq_balance code? If so, I think you'll only use
1 cpu to process all the interrupts from each gigabit card. Not that
you have much choice, since Intel broke the P4's interrupt routing.

Which of the e1000 modules settings did you play with? tx_delay
and rx_delay? What rev of the e1000 chipset?

M.