Where is TCP processed - CPU? Networkinterface? Elsewhere?

[chemlud]

Hi, have a problem that bugs me for years, no solution found yet:

Two clients with Linux, same update status:

1. SLOW: Libretrend i7 with Coreboot, Realtek NIC

2. FAST: Old Dell Precision M6500 notebook with Intel NIC.

Problem: when downloading e.g. updates, the FAST ist 30-times faster than SLOW, see attached.

Same mirrors,RJ45 cables changed twice, both attached to the same switch. So no real explanation.

Yesterday I did some iperf between the two clients.

For UDP, it does not matter, which is server and whicch is client:

20260118145326,SLOW,FAST,45678,1,0.0-30.0,3935190,1048952,0.025,0,2677,0.000,0

20260118145446,FAST,SLOW,45678,1,0.0-30.0,3935190,1048950,-nan,0,-1,-0.000,0

But for TCP direction matters:

20260118144505,SLOW,FAST,45678,1,0.0-30.0,3533963328,941434163

20260118144740,FAST,SLOW,45678,1,0.0-30.1,1690173504,449722645

-------------------------

First thought: RJ45 in SLOW machine is Realtek. But I have Realtek in other machines with same linux, always maxing out the bandwith possible. So I don't think it'S simply Realtek.

Why only TCP makes a difference? Is there offloading and that doesn't work properly in the SLOW machine? Maybe due to Coreboot?

Any ideas how this difference in TCP-speed might be explainable?

:-)

[Seimus]

Your topic name is a bit intriguing.
When you think about a packet, the finial destination on a device is the CPU. If a packet is delivered its being pegged to the CPU to process it. Of cource the packet needs to be 1st processed on the NIC.

What Distro you are using?
What realtek NIC does it use?
What is the realtek driver loaded for the NIC?
Did you try to upgrade the BIOS?
What are the temps during high volume downloads/uploads?
Can you post the NIC statistics (counters)?
Did you disabled ASPM?

Regards,
S.

[chemlud]

1 What Distro you are using?
2 What realtek NIC does it use?
3 What is the realtek driver loaded for the NIC?
4 Did you try to upgrade the BIOS?
5 What are the temps during high volume downloads/uploads?
6 Can you post the NIC statistics (counters)?
7 Did you disabled ASPM?

1 opensuse Tumbleweed

2 01:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller (rev 07)
  Subsystem: Realtek Semiconductor Co., Ltd. RTL8111/8168 PCI Express Gigabit Ethernet controller

3 Kernel driver in use: r8169
  Kernel modules: r8169

4 Yes, but it's Coreboot, the company Libretrend dose not provide any newer Coreboot version

5 Unremarkable temps, cooling is appropriate

6 like this? On the SLOW i have:
   

Code Select Expand

sudo ethtool -S eth0
    NIC statistics:
    tx_packets: 3175999
    rx_packets: 8314948
    tx_errors: 0
    rx_errors: 0
    rx_missed: 36
    align_errors: 0
    tx_single_collisions: 0
    tx_multi_collisions: 0
    unicast: 8313262
    broadcast: 1686
    multicast: 0
    tx_aborted: 0
    tx_underrun: 0
7 No. It's an onboard NIC, so relevant?
   

Code Select Expand

sudo ethtool --show-eee eth0 
    EEE settings for eth0:
    enabled - inactive
    0 (us)
        Supported EEE link modes:  100baseT/Full
                                  1000baseT/Full
        Advertised EEE link modes:  100baseT/Full
                                    1000baseT/Full
        Link partner advertised EEE link modes:  Not reported

[chemlud]

To make things even more complicated:

- I downloaded a large file on SLOW with FF 147.0 and get an amazing 100MB/s...

What's going on here? Only the weekly updates of Tumbleweed slow?!?! But it's not the server, see OP.