The MaxReadRequest size is set too low (512 bytes)

At the end of the OFED installation, I receive this advice:

Device (41:00.0):

41:00.0 Network controller: Mellanox Technologies MT27500 Family [ConnectX-3]

WARNING - device 41:00.0 The MaxReadRequest size is set too low (512 bytes) and will affect performance.

Please consult your server’s vendor and if possible change BIOS settings or use setpci to configure MaxReadReq to 4096 bytes.

/usr/bin/setpci -s 41:00.0 68.W


Change to 4096 bytes:

/usr/bin/setpci -s 41:00.0 68.W=5xxx

The current value is:

$ sudo /usr/bin/setpci -s 41:00.0 68.W


I don’t see a relevant BIOS setting ( Poweredge C6145 ), so considering the setpci route.

So I assume the advice would be to do the following (I haven’t yet):

$ sudo /usr/bin/setpci -s 41:00.0 68.W=5000

Reading elsewhere ( setup MaxReadReq to 4096 bytes definitely ) it seems this isn’t a permanent solution, and something similar can done by setting ib_mthca tune_pci=1 in /etc/modprobe.conf. What’s the preferred solution to fix the MaxReadRequest issue?

Hi Matt,

Currently the correct way is as you say, change it with setpci. the recommended values for ConnectX-3 are :

Max Payload size - 256

Max Read Request - 4096

Hi Matt,

There is (or at least used to be) a variable in the .ini configuration file where you could set this. The variable was ‘default_max_read_request_size’. I’ll have to check to see if this is still active. Thanks.