[nvme(t)-rdma Question] Understanding nvmet_port's max_queue_size

[Jigao Luo]

Hi nvme-rdma experts,

I’m trying to understand the queue size (max_queue_size) for NVMe-oF 
over RDMA. I came across the max_queue_size field in the struct 
nvmet_port, which appears to be capped at the max value: 
NVME_RDMA_MAX_QUEUE_SIZE.

First Question:
I would like to confirm my understanding of this setting: The 
max_queue_size is configured on the NVMe-oF target when setting up ports 
for NVMe subsystems. Once set, if an NVMe-oF host connects and runs FIO 
on the nvmeof device, my assumption is that an iodepth specified in FIO 
that is larger than the target’s max_queue_size will not be fully 
utilized. Is this assumption correct? Alternatively, could having an FIO 
iodepth larger than the target’s max_queue_size negatively impact 
performance due to this mismatch in queue depths?

Second Question:
I noticed that this patch set enables max_queue_size in the 
configuration entry and increases the max value from 128 to 256: 
https://lists.infradead.org/pipermail/linux-nvme/2024-January/044145.html
My current kernel and driver versions are earlier than this patch (mine 
is Linux 6.6.1). Is there any way for old kernel to view the current 
max_queue_size value? I’ve checked via dmesg and 
/sys/kernel/config/nvmet/ports/, but I don’t see any reference to 
max_queue_size.


Thank you for your assistance and insights!

Best regards,
Jigao