NonStop S-Series Server Description Manual (G06.24+)

Interprocessor Communication

HP NonStop S-Series Server Description Manual—520331-003

9-12

Request With Short Request Data

A request phase that includes short-length request data (Figure 9-6) makes temporary

use of pre-push buffers to transfer data from a linker’s buffer to a listener’s buffer. This

transfer method is used when the total length of control information and data does not

exceed the size of a pre-push buffer, currently 512 bytes. Because the addresses of

these buffers are static and known to the message systems in each processor, the

transfer can proceed without the linker knowing the ultimate location of the listener’s

destination buffer.

In the first part of this phase (upper part of Figure 9-6), all of the request information

and the request data is sent from the linker to the listener as a single message. For this

message, the message system creates a TIB (1), using the ServerNet address of one

of the four pre-push buffers known to exist in the listener’s processor specially for this

(the linker’s) processor. ServerNet services translates the TIB to BTE descriptors (2),

and transfers control to the BTE.

The BTE (3) pre-pushes the request control information first, then all of the data, and

lastly transmits the request setup packet. Each packet is transmitted over the

ServerNet hardware (4) to the AVT hardware in the listener processor, where it is sent

to one of two destinations (5). The control information and the data are sent to the

addressed pre-push buffer and the final packet, the setup, is linked into the interrupt

queue.

When the interrupt is processed, the message system transfers the setup information

to an MQC in the readlink cache (6), as well as the control information and all the data

(7). The message system then alerts the listener process that the message has been

received.

In the second part of this phase (lower part of Figure 9-6), the listener process calls the

message system with MSG_READCONTROL_ and MSG_READDATA_ to copy the

control information and data in the MQC in the readlink cache to corresponding buffers

(8 and 9). The listener process might have allocated these buffers previously or could

do so at this point.