[Users] How to make Mellanox ports use different IRQ lines?

[Adhiraj Joshi]

Hi all,

We have a kernel module through which we do RDMA data transfer using Mellanox cards. We find that at the receiver side, when we use two IB ports of the same Mellanox card, the interrupts (RDMA write completion events) occur only on one IRQ line as seen from "cat /proc/interrupts | grep mlx" (first IRQ line of that adapter, when we can see that there are total 3 IRQ lines mlx4-comp-0, mlx4-comp-1, mlx4-comp-2). This severely affects the performance of the applications used by our customers. When we use two IB ports from two different cards, we can see that interrupts are evenly spread across 2 IRQ lines (again, mlx4-comp-0 of both the adapters gets used) and so we can map these two IRQ lines to two CPUs and get parallelism.

Any idea/pointers on why two different IRQ lines do not get used for the ports of the same adapter?

Regards,
Adhiraj.
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