Extend range of communicator IDs for the RDMA protocol #367
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This is changing the msgbuff so that it can support any number of bits for the sequence number, not just 16. This is in preparation to increase the range of comm IDs, which requires changing the number of bits used for the msg_seq_num. To fit a larger comm ID in the immediate data, the message sequence number bit-width must be reduced. With the 16 bits msg_seq_num the msgbuff relied on the wraparound of 16 bits integers, so to reduce the number of bits of msg_seq_num we need to make the wrapping around explicit and implement a distance function to deal with the wraparound case. This makes the msgbuff more generic, as it can now support any msg_seq_num space and any number of inflight messages, as long as they are powers of 2. This also extended the msgbuff unit test to test the case when message sequence numbers wrap around. Signed-off-by: Amedeo Sapio <[email protected]>
Changing the number of bits used for the communicator ID from 12 to 18 to reduce the chance of running out of comm IDs. To fit a larger comm ID in the immediate data, the message sequence number has been reduced from 16 bits to 10, which is still more than enough since usually the number of inflight messages is not that high. The msg_seq_num space can be further reduced if needed. Signed-off-by: Amedeo Sapio <[email protected]>
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Issue
The RDMA protocol is currently using 12 bits for the communicator ID, limiting the number of communicators to 4K, which can be hit in large deployments.
Description of changes:
This PR is hanging the number of bits used for the communicator ID from 12 to 18 to reduce
the chance of running out of comm IDs. To fit the comm ID in the immediate data,
the message sequence number has been reduced from 16 bits to 10, which is still
more than enough since usually the number of inflight messages is not that high.
The msg_seq_num space can be further reduced if needed.
With the 16 bits msg_seq_num the msgbuff relied on the wraparound of 16 bits integers,
so to reduce the number of bits of msg_seq_num we need to make the wrapping around
explicit and implement a subtraction to deal with the wraparound case. This makes
the msgbuff more generic, as it can now support any msg_seq_num space and any
number of inflight messages (not only powers of 2).
The msgbuff unit test has also been extended to test the case when message sequence numbers wrap around.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.