[TriLUG] Problem determination help needed

[David Both via TriLUG]

I have been trying to determine the cause of a networking speed problem 
for months now and have narrowed it down considerably. But I would like to 
know why this is occurring and whether it can be fixed or circumvented.

I have a Fedora 33 host with the following hardware:

#######################################################################
# Machine Type: 	physical machine.
# Host architecture: 	X86_64
# Motherboard Mfr: 	ASUSTeK COMPUTER INC.
# Motherboard Model: 	PRIME H370M-PLUS
# Motherboard Serial: 	190550974401411
#----------------------------------------------------------------------
# CPU Model:		Intel(R) Core(TM) i5-9400 CPU @ 2.90GHz
# CPU Data:		1 Six Core package with 6 CPUs
# CPU Architechture:	x86_64
# HyperThreading:	No
# Max CPU MHz:		4100.0000
# Current CPU MHz:	3900.004
#----------------------------------------------------------------------
# RAM:			31.205 GB
# SWAP:			11.999 GB
#----------------------------------------------------------------------
# Install Date:		Tue 27 Oct 2020 12:57:13 PM EDT
# Linux Distribution:	Fedora 33 (Thirty Three) X86_64
# Kernel Version:	5.9.16-200.fc33.x86_64
######################################################################


It also has three PCIx NICs that I use to route between my AT&T internet 
connection, my privatez internal network, and a wireless router. This 
keeps things separated nicely by using IPTables to determine routing based 
on source network and port.

My internal network gets well over 900 Mb/s connectivity to the outside 
world using Oookla speedtest. This is very consistent and I have come up 
with similar numbers based on some large file transfers.

The problem is with the NIC connected to the wireless router - I have 
trioed a couple different TP-Link 5G routers with 4-port Gb switches. I 
get only about 350Mb/s when using a wired connection through the physical 
Gb switch on the router. I also eliminated the router by connecting my 
laptop directly to the "slow" NIC. I have also replaced the NIC with a 
brand new one. All three NICs are identical TP-Link PCIx Gb devices.

I have use tools like iotop, glances, htop, and others and there is 
minimal IO wait, lots of free RAM for cache and buffer space, plenty of 
available CPU, so I am at a loss.

Does anyone have any ideas why this might be happening? Is it a PCI bus 
limit?

Thanks in advance for any ideas.



-- 


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David P. Both, RHCE
He/Him/His
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www.both.org - My personal web site
www.Linux-Databook.info - Home of the DataBook for Linux
DataBook is a Registered Trademark of David Both
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The value of any software lies in its usefulness
not in its price.

— Linus Torvalds
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