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Orangutanklaus 11-08-2010 02:04 PM

GbE throughput doesn't satisfy me
Hiho mates!

I'm running a Zotac NM-10-B-E (equipped with a D510 ATOM cpu and 4GB of RAM) under Ubuntu 10.10 x64. The system is connected to a suitable GbE switch from Linksys. Because the ATOM machine is currently only a testbed the operating system is installed on a SDHC via USB. The workmate on the LAN is a powerfull six core machine, running Win7 x64.

The connection tests are performed with the current versions of iperf. The problem - I can't exeed ~0.5Gbit throughput. File transfer tests from and to a local ramdisk on the linux system confirm the result from iperf. All tests were performed trough a direct connection as well.

The cpu workload moves arround 70% while the NIC is transfering/receiving data. The settings on the linux systems for tcp autotuning seem to be sensible. Enough buffer space as well as all advanced setings like selective ACKs, window scaling and so on are active.

In my eyes the linux system, more precise the ATOM, should be capable to handle nearly full speed GbE throughput - at last in synthetic benchmarks like iperf. Could it be a problem of the driver implementation for the NIC?

03:0b.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8110SC/8169SC Gigabit Ethernet (rev 10)
        Subsystem: ZOTAC International (MCO) Ltd. Device 8167
        Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 16
        I/O ports at e800 [size=256]
        Memory at febdfc00 (32-bit, non-prefetchable) [size=256]
        Expansion ROM at febe0000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: r8169
        Kernel modules: r8169

Any suggestions are welcome!


paulsm4 11-09-2010 11:47 PM

Hi -

Two suggestions:
1. Check out this link:

2. Consider trying a different type of GB Ethernet card. There are many good choices on the LQ HCL:

'Hope that helps!

Orangutanklaus 11-10-2010 03:07 AM

I've tried your first suggestion adopt to my ubuntu system but with no success. After studying the specification for this NIC at Realtek's website I recogniced that the RTL-8110SC/8169SC Gigabit Ethernet (rev 10) has only a PCI interface for the connection to the chipset. After all tests and configurations I believe this must be the reason for the minor throughput as we know PCI is at best capable to handle this bandwidth theoratical.

So I don't spend more time in this problem and going to buy a PCIe NIC. That really annoying me because it discards my whole concept but I see no other solution to get full GbE throughput.

Anyway, thank you for your reply and tips.


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