In their default configuration, the Mellanox Connext2 NICs enforce a lower limit on timeouts (specifically, the IBV_QP_TIMEOUT option). With this limit, you cannot set a timeout value less than about 500ms. Combined with the default setting of 7 retries, this means that after a timeout (e.g., a crashed server) the transmit buffer is held by the NIC for about 4 seconds before it is returned with an error. This can cause RAMCloud to run out of transmit buffers. To fix the problem, we modified the firmware in our NICs. Here is how we did it:
- Get from Mellanox the appropriate version of the firmware to start with. For our ConnectX2 NICs (as of December 2012) this file is in ~ouster/samba/mellanox/fw-ConnectX2-rel.mlx.
This file needs to be combined with an appropriate .ini file. First, fetch the existing .ini file from the NIC:
flint -d /dev/mst/mt26428_pci_cr0 dc > mt26428.ini
flint -d /dev/mst/mt26428_pci_cr0 dc > mt26428.ini