CODEWITHSUNDEEP
rdmainfiniband
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rafoo

Reputation: 1642

Should I use volatile with RDMA buffers?

I am learning RDMA verbs in C (libibverbs).

One question I have is after having polled a Receive Work Completion with a Receive RDMA write with immediate (IBV_WC_RECV_RDMA_WITH_IMM), the compiler might not see that the content of the receiving buffer has changed. So, do we need to declare the receiving buffer volatile? AFAI, this is one usage of volatile: the content of the variable can be modified by an external source (here, RDMA hardware).

An example of code:

void receive(volatile char* receiving_buffer, size_t size, ibv_cq *cq)
{
    ibv_wc wc;
    int n = 0;
    while(n == 0) n = ibv_poll_cq(cq, 1, &wc);

    assert(wc.status == IBV_WC_SUCCESS);
    assert(wc.opcode == IBV_WC_RDMA_WRITE && (wc.wc_flags & IBV_WC_WITH_IMM));

    // Prevent buffer overflow
    receiving_buffer[size - 1] = '\0';

    printf("%s\n", receiving_buffer);    
}

Is qualifying receiving_buffer with volatile needed?

I guess the answer will be the same for RDMA write or RDMA send.

Upvotes: 0

Views: 58

Answers (0)

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