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

Interprocessor Communication

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

9-14

Request With Medium Request Data

When the combination of request control and data is too big to fit in the pre-push

buffers but small enough to fit in a readlink cache buffer (Figure 9-7), the message

system eliminates use of the pre-push buffers (shown in Figure 9-6 on page 9-13).

Instead, the message system causes the listener process to reverse roles and to pull

the data to itself, using ServerNet response packets to transfer data from a linker’s

buffer to the listener’s readlink cache. (In the two preceding topics, data was sent in

ServerNet request packets—that is, pushed.)

In the first part of this phase (upper part of Figure 9-7), only the setup information is

sent from the linker to the listener. This is done as a single-packet message. For this

message, the message system creates a TIB (1), and ServerNet services translates

the TIB to BTE descriptors (2). ServerNet services transfers control to the BTE (3),

which transmits the request setup packet (4) to the AVT hardware in the listener

processor. There, the setup is linked into the interrupt queue (5).

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

stores it in an MQC in the readlink cache (6), and recognizes that this request contains

request data of medium length. It consequently recognizes that it has to pull the

request data.

In the next part of this phase (middle part of Figure 9-7), the listener’s message system

creates a TIB (7) in preparation for the pull. ServerNet services then translates the TIB

to BTE descriptors (8) and transfers control to the BTE (9). The BTE in the listener

then proceeds to issue read request packets to the AVT in the linker processor (10),

which in corresponding response packets, transmits the original request control

information, followed by the request data (11). The response packets go back to the

listener BTE (12) for temporary storage in the readlink cache (13).

In the third part of this phase (lower part of Figure 9-7), 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

(14 and 15).