SGI Altix cross partition functionality

Terminology

The term 'partition', adopted by the SGI hardware designers and which perculated up into the software, is used in reference to a single SSI when multiple SSIs are running on a single Altix. An Altix running multiple SSIs is said to be 'partitioned', whereas one that is running only a single SSI is said to be 'unpartitioned'.

The term '[a]cross partition' refers to a functionality that spans between two SSIs on a multi-SSI Altix. ('XP' is its abbreviation.)

Introduction

This feature provides cross partition functionality when running multiple partitions on a single SGI Altix.

This functionality includes such things as a pseudo-ethernet driver and memory sharing, which are provided by functional support modules that sit on top of a low-level communication module.

The communication module provides channels for point-to-point communication between the partitions. There is support for eight channels between any two partitions (currently only two channels are in use, the remainder are available for possible future expansion). A functional support module uses the same channel number for all of its cross partition communication across the entire Altix.

There is a shim module that acts as an interface between the functional support modules and the communication module. Its sole purpose is to allow for the communication module to be rmmod'd/insmod'd without 'disturbing' the functional support modules and the user processes utilizing them. The shim module has also proven itself to be invaluable for debugging.

This feature is being submitted as four separate quilt patches:

    exports  - symbols that need to be exported for XP[C|NET]
    XP       - shim module
    XPC      - cross partition (low-level) communication module
    XPNET    - cross partition pseudo-ethernet driver functional support module

The XPC patch is dependent on the SGI fetchop driver patch to be applied first. The SGI fetchop driver patch is being pushed out to the community separately by Dean Roe.

The XPC patch is also dependent on bte_copy(). This function activates the SGI Altix's Block Transfer Engine (BTE).