[SPDK] The low water mark in NVMe/TCP target

[SPDK] The low water mark in NVMe/TCP target

[Bin Yang]

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Hello, Everyone!

I find spdk set low water mark in NVMe/TCP target to 8 bytes (sizeof(struct spdk_nvme_tcp_common_pdu_hdr))
In my test case, sometimes, there might be very small data packet (as small as 4 bytes) be sent to wire，After
this, if there is no more data sent to the same socket, this small data packet won’t be received by NVMe/TCP controller qpair poll，
because the size hasn’t reached the low watermark.

So I want to know:

1)    Why spdk need to set low watermark in NVMe/TCP target to 8 bytes，I don't think there's much advantage in doing that?

2)    Can we set low watermark in NVMe/TCP target to 1 bytes just like iscsi target_does?

Thanks,

Bin