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I am seeing an issue with NFSv4 performance on Ubuntu 20.04.3 LTS on both
clients and server (tested kernels 5.4 to 5.16), where the server is connected
by 10Gbit Ethernet and with multiple clients connected by 1Gbit. I am reading a
large file from an NFS mount via "dd" sending output to /dev/null with bs=4096.
Using default sysctl and mount options I am seeing speeds maxing out below
1Gbit/sec. If I force NFSv3 I see speeds close to 10Gbit/sec with sufficient
clients connected. I also see no issue with Ubuntu 16.04 (when used for both
server and clients) in conjunction with NFSv4. I have attached the output from
two iftop's which shows the status when using NFSv4 and when using NFSv3, in
the NFSv4 you can clearly see one client reading at max speed and all the
others apparently throttling back to practically nothing.
I have additionally tested a range of mount options, which made no difference,
BBR congestion control which made no difference and the following kernel
settings which also made no difference:
net.core.netdev_max_backlog=250000
net.core.rmem_max=4194304
net.core.wmem_max=4194304
net.core.rmem_default=4194304
net.core.wmem_default=4194304
net.core.optmem_max=4194304
net.ipv4.tcp_rmem=4096 87380 4194304
net.ipv4.tcp_wmem=4096 65536 4194304
net.ipv4.tcp_mem=786432 1048576 26777216
net.ipv4.udp_mem=1529892 2039859 3059784
net.ipv4.udp_rmem_min=16384
net.ipv4.udp_wmem_min=16384
The problem is seen on dissimilar hardware, ie this problem exists when
testing with an HP DL380 G10 with Mellanox 10Gbit Ethernet connected to
Cisco switch, and also on a Dell R430 with Broadcom 10Gbit Ethernet
connected to a Netgear switch (just to name two of several
configurations that have been tested). The clients vary in each test
case also, but are desktop PCs and laptops.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: bot-comment
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NFSv4 performance problem with newer kernels
https://bugs.launchpad.net/bugs/1960826
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