What's the doorbell in InfiniBand?

Question

I am reading a document ablut InfiniBand, which is called 《InfiniBand™ Host Channel Adapter Verb Implementer’s Guide》--Intel, in Chapter 6.2.2, it mentions a concept called "Doorbell", I haven't found any information about this concept in the IB specification. I wonder if the doorbell is a notification mechnism or something else? Is there something detail about it? Thank you!

Answer 1

The definition is two sections further up under 6.2:

Protection domain is used as a form of access security for memory regions, address vectors and queue pairs as defined by the InfiniBand Architecture. The Architecture requires a protection domain before a QP is allocated. Most vendors who expect to support user mode IO, will have a form of notification handshake from user mode. In most HCA’s this is a device memory address mapped to the process address space. We call this address the “doorbell” in this document.

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