TMF Reference Manual (G06.26+)

TMFCOM Commands
HP NonStop TMF Reference Manual—522418-003
3-117
ALTER TMF
In general, the factors that can determine whether MMI can improve performance on
your system are:
•
The number of processors on the node.
•
The average number of processors that participate in a transaction.
Because MMI contacts fewer processors than the standard flush protocol does, MMI
reduces the total number of messages that must be transmitted between processors
on behalf of a distributed transaction. This benefit, however, comes at the cost of the
overhead that MMI must perform to do its work while it is enabled. For small systems,
the reduction in number of messages may not be enough to offset MMI’s impact on
performance. But for large systems, the reduction may be so great that MMI can offer
a significant performance gain.
You can use the GOREMOTE option to direct TMF to use either the PIO mechanism or
the Message System to send GoRemote requests to the TMP. GoRemote requests
are initiated by the File System on the parent node when the File System determines
that a transaction must be distributed to another node. The GoRemote requests
contain the transaction ID. The GoRemote requests are sent to the TMP on the parent
node, which transmits them to the child node for use there.
If the TMP resides on a processor other than the one where the distributed transaction
originated, the GoRemote request must be sent to the TMP through an interprocessor
message. Most TMF interprocessor messages use PIOs. PIOs are low-level, very fast
messages. In addition, TMF uses a “box-carring” protocol that buffers the PIOs to
improve transaction throughput. This improvement occurs not only because the
buffering is more efficient, but also because the improvement reduces response time
because the buffer content can be transmitted either when the buffer is full or when the
TMP’s wait-timer expires (depending on the setting established by the PIOBUFFER
option of the ALTER TMF command). In the TMP’s processor, the Bus Receive
interrupt handler receives the PIO, unpacks to GoRemote request, and queues the
Goremote request against the TMP. You can direct TMF to use the PIO mechanism to
transmit GoRemote requests to the TMP by specifying the GOREMOTE PIO option or
GOREMOTE PIOPRIORITY option in the ALTER TMF command.
Unless the TMP wait timer is OFF, the TMP processes the incoming GoRemote
request when the TMP wait timer expires. This method can introduce an additional
delay but, like PIO buffering, this method generally results in improved throughput.
In contrast, when GoRemote messages are sent though the Message System, no
buffering occurs, no timers are involved, and the TMP wakes automatically. Setting
GoRemote to MSG may improve network transaction response time and throughput
because GoRemote messages are processed independently of transaction
completions.