Cell software development: Difference between revisions

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'''Software development''' for the [[cellCell microprocessor]] involveinvolves a mixture of conventional development practices for the [[IBM POWER|POWER architecturePowerPC]]-compatible PPU core, and novel software development challenges with regardsregard to the functionally reduced SPU coprocessors.

==CellLinux SDKon Cell==

An open source software-based strategy was adopted to accelerate the development of a Cell BE ecosystem and to provide an environment to develop Cell applications, including a GCC-based Cell compiler, binutils and a port of the Linux operating system.<ref name="research.ibm.com">{{cite web|url=http://www.research.ibm.com/people/m/mikeg/papers/2007_ieeecomputer.pdf|format=PDF|title=An Open Source Environment for Cell Broadband Engine System Software|date=June 2007}}</ref>

{{Cell microprocessor segments}}

===Full system simulator===

===GNU compiler toolchain===

===IBM XL C/C++===

===IBM Octopiler===

====References====

<!-- Correction: This article misstated the nature of the processor core in IBM's Cell. The processor core uses the same instruction set as the PowerPC 970, therefore letting it run the same software. The core is a fellow member of IBM's PowerPC AS family, but is not a PowerPC 970. -->

* International Symposium on Code Generation and Optimization (CGO'06)

==Linux on cellOctopiler==

'''Octopiler''' is [[IBM]]'s prototype [[compiler]] to allow [[software developer]]s to write [[software code|code]] for [[Cell processor]]s.<ref>{{citation|title=Using advanced compiler technology to exploit the performance of the Cell Broadband Engine architecture|date=2017-10-23|url=http://www.research.ibm.com/journal/sj/451/eichenberger.html|archive-url=https://web.archive.org/web/20060411094457/http://www.research.ibm.com/journal/sj/451/eichenberger.html|archive-date=2006-04-11|url-status=dead|publisher=IBM Systems Journal}}</ref><ref>{{Cite web|date=2006-01-20|title=Compiler Technology for Scalable Architectures|url=https://www.empat.tech/services|archive-url=https://web.archive.org/web/20080320071448/http://domino.research.ibm.com/comm/research_projects.nsf/pages/cellcompiler.index.html|archive-date=2008-03-20|access-date=2025-06-11|website=IBM Research|language=en-us}}</ref><ref>{{Cite web|last=Stokes|first=Jon|date=2006-02-26|title=IBM's Octopiler, or, why the PS3 is running late|url=https://arstechnica.com/uncategorized/2006/02/6265-2/|access-date=2025-06-11|website=Ars Technica}}</ref>

An open source software-based strategy was adopted to accelerate the development of a Cell BE ecosystem and to provide an environment to develop Cell applications, including a GCC-based Cell compiler, binutils and a port of the Linux operating system.<ref name="research.ibm.com">{{cite web|url=http://www.research.ibm.com/people/m/mikeg/papers/2007_ieeecomputer.pdf|format=PDF|title=An Open Source Environment for Cell Broadband Engine System Software|date=June 2007}}</ref>

==Software portability==

===Adapting VMX for SPU===

====Differences between VMX and SPU====

The [[AltiVec|VMX]] (Vector Multimedia Extensions) technology is conceptually similar to the [[vector model]] provided by the [[SPU processors]], but there are many significant differences.

{| class="wikitable" style="margin: 1em auto 1em auto"

|+ '''VMX to SPU Comparison'''{{ref|vmxrefman}}<!-- 333 pages --><br>''unfinished''

! feature || VMX || SPU

|-

! [[word (computer science)|word]] size

| 32 bits || 32 bits

|-

! number of [[register (computer science)|registers]]

| 32 <!-- p.28/333 --> || 128

<!-- p.34/333 also shows 32 GP and 32 FP regs, are these part of VMX? -->

|-

! [[wordWord (computerdata sciencetype)|word]] size

! register width

| 32 bits || 32 bits

| 128 bit quadword <!-- p.28/333 --> || 128 bit quadword

|-

! number of [[Processor register (computer science)|registers]]

! [[integer]] formats

| 32 <!-- p.28/333 --> || 128

<!-- p.34/333 also shows 32 GP and 32 FP regs, are these part of VMX? -->

|-

! register width

| 128 -bit quadword <!-- p.28/333 --> || 128 -bit quadword

|-

! [[integer]] formats

| 8, 16, 32 <!-- p.26/333 --> || 8, 16, 32, 64 <!-- checked: there is no doubleword add or mul instr. -->

|-

! saturation support

| yes <!-- p.26/333 --> || no <!-- check this -->

|-

! byte ordering

| big (default), little <!--p.44/333 --> || big endian

|-

! byte ordering

! [[floating point (computer science)|floating point]] modes

| big (default), little <!--p.44/333 --> || big endian

|-

! [[floating Floating-point (computer science)arithmetic|floating point]] modes

| Java, non-Java || single precision, IEEE double

|-

! [[memoryData (computerstructure science)alignment|memory]]Memory alignment ]]

| quadword only || quadword only

|}

The VMX ''[[Java (programming language)|Java]] mode'' conforms to the [[Java Language Specification]] 1 subset of the default [[IEEE Standard]], extended to include IEEE and [[C99|C9X]] compliance where the Java standard falls silent. In a typical implementation, non-javaJava mode converts [[denormal]] values to zero but javaJava mode traps into an emulator when the [[processor (computer science)|processor]] encounters such a value. ''Non-Java mode'' might or might not be faster, might or might not be non-compliant.

The IBM ''PPE Vector/SIMD manual'' does not define operations for double -precision floating point, though IBM has published material implying certain double -precision performance numbers associated with the Cell PPE VMX technology.

Quadword (ie Four times a 32 bit word or 128 bits) alignment is on 16 Byte (128 bit) boundaries (ie the low four address bits are zero).

The IBM ''PPE Vector/SIMD manual'' does not define operations for double precision floating point, though IBM has published material implying certain double precision performance numbers associated with the Cell PPE VMX technology.

====Intrinsics====

ThisCompilers featurefor isCell{{Who|date=February used2011}} toprovide have[[intrinsic SPU'function|intrinsic]]s assemblyto languageexpose useful SPU instructions in C/ and C++. Instructions that differ only onin the type of operand (such as a, ai, ah, ahi, fa, and dfa for addition) are typically represented by a single C/C++ intrinsic which selects the proper instruction based on the type of the operand.

====Porting VMX code for SPU====

ThereA issubstantial a great bodyamount of codeVMX which([[Altivec]]) has beencode developed for other [[IBM [[Power processorsmicroprocessors]], that could potentially be adapted and recompiled to run on the SPU. This code base includes VMX code that runsparticularly under the [[PowerPC]] version of [[Apple Computer|Apple'smacOS]], [[Maccan OSpotentially X]],be whereadapted itfor isuse betteron knownthe as [[Altivec]]SPU. DependingThe onfeasibility howof manyporting VMXdepends specific features are involved,on the adaptationextent involvedof canVMX-specific rangefeatures anywhereused—ranging from straightforward, to onerous, to completely impractical. TheHowever, most importantkey workloads fortypically themap SPUwell generallyto mapthe quiteSPU wellarchitecture.

In some cases it is possible to port, existing VMX code can be ported directly. If the VMX code is highly generic (makes few assumptions about the execution environment) the translation can be relatively straightforward. The two processors specify a different [[binary format|binary code format]], so recompilation is required at a minimum. Even where [[Instruction (computer science)|instructions]] exist with the same behavioursbehaviors, they do not have the same instruction names, so this must be mapped as well. IBM's providesdevelopment toolkit includes compiler intrinsics whichthat takeautomate caremuch of this mapping transparently as part of the development toolkit.

In many cases, however, a directly equivalent instruction does not exist. The workaround might be obvious or it might not. For example, if saturation behaviourbehavior is required on the SPU, it can be coded by adding additional SPU instructions to accomplish this (with some loss of efficiency). At the other extreme, if Java floating -point semantics are required, this is almost impossible to achieve on the SPU processor. To achieve the same [[computation]] on the SPU might require that an entirely different [[algorithm]] which needs to be written from scratch.

The most important conceptual similarity between VMX and the SPU architecture is supporting the same [[vectorization model]]. For this reason, most algorithms successfully adapted to Altivec will usually adapt successfully to the SPU architecture as well.

==Local store exploitation==

LocalTransferring data between the local stores of different SPUs can have a large performance cost. The local stores of individual SPUs can be exploited using a variety of strategies.

Applications with high locality, such as dense matrix computations, represent an ideal workload class for the local stores in Cell BE.<ref>{{cite web|url=http://www.research.ibm.com/people/m/mikeg/papers/2006_ieeemicro.pdf|title=Synergistic Processing in Cell's Multicore Architecture|date=March 2006}}</ref>

<ref>{{cite web|url=http://www.research.ibm.com/people/m/mikeg/papers/2006_ieeemicro.pdf|format=PDF|title=Synergistic Processing in Cell's Multicore Architecture|date=March 2006}}</ref>

Streaming computations can be efficiently accommodated using [[software- pipelining]] of memory block transfers using a multi-buffering strategy.<ref name="research.ibm.com"/>

The software cache offers a solution for random accesses.<ref>{{cite web|url=http://www.research.ibm.com/journal/sj/451/eichenberger.pdf|format=PDF|title=Using advanced compiler technology to exploit the performance of the Cell Broadband Engine architecture|date=January 2006}}</ref>

More sophisticated applications can use multiple strategies for different data types.<ref>{{cite web|url=http://www.research.ibm.com/cell/papers/2008_vee_cellgc.pdf|format=PDF|title=Cell GC: Using the Cell Synergistic Processor as a Garbage Collection Coprocessor |date=March 2008}}</ref>

====References====

==Compiler-mediated parallelism==

===References===

* [http://www.research.ibm.com/cell/ The Cell Project at IBM Research]

* [http://cag.csail.mit.edu/crg/papers/eichenberger05cell.pdf Optimizing Compiler for a CELL Processor]

* [httphttps://wwwdx.researchdoi.ibmorg/10.com/journal1147/sj/.451/eichenberger.html0059 Using advanced compiler technology to exploit the performance of the Cell Broadband Engine architecture] <!-- repackaging of Eichberger ''et al.'' above -->

* [http://domino.research.ibm.com/comm/research_projects.nsf/pages/cellcompiler.index.html Compiler Technology for Scalable Architectures]

{{reflist}}

{{Cell microprocessor segments}}

==References==

<references/>

{{DEFAULTSORT:Cell Software Development}}

[[Category:Cell BE architecture]]

[[Category:Compilers]]

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