SAPonPower

An ongoing discussion about SAP infrastructure

Questions about Linux on Power and HANA on Power

A curious reader just posed some questions that I suspect many more of you also have.  Here are the questions posed, and my answers:

 

“I remember at a trade show some years ago asking on the IBM stand how you ran Linux on a mainframe. I was told that whilst the SLES distribution had to be recompiled you could actually run compiled x86 Linux binaries on the mainframe. I thought that was pretty clever as getting all the ISVs to recompile for Linux on a mainframe would be a nightmare.

Coming to Linux on Power the web site is unclear whether you can run compiled x86 Linux binaries on Power. I suspected that the PowerVM hypervisor may be able to emulate the Intel instructions and run the x86 binaries, but is isn’t very clear.”

Both RedHat and SUSE Linux are operating systems which have been compiled to run on the Power platform.  The vast majority of the operating system code is identical across Power and x86 versions with only the low level code that directly interacts with the hardware being unique to the specific platform.  Currently, both run in big endian (BE) mode (byte order on disk and memory as opposed to x86 systems which run in little endian (LE); no positive or negative effect for either, simply a design choice).  As such, most applications running in those environments today require are compiled natively, not running with any emulation.  IBM did offer a “binary translation” function in 2011 called Lx86 which allowed x86 Linux applications to run unmodified on Linux on Power, but it was not widely adopted and was later removed from marketing in 2013.  In May, 2014, IBM announced that it would support the software based KVM as an alternative to the hardware/firmware hypervisor.  This allows customers that want to have a single set of administrative tools and skills to utilize KVM on both Power and x86 environment.  It also enables more OSs to run on Power as with KVM,  the system may be run in LE mode.  Canonical Ubuntu is now available on Power and is the first Linux OS to run in LE mode.  Both RedHat and SUSE are also available to run under KVM, however they currently run only in BE mode with SUSE planning on delivering a LE version (SLES 12) in the near future.  Debian and openSUSE are also reportedly working on LE versions for the Power platform.   Currently, LE is only supported under KVM and the entire system must run in the same mode.  In the future, IBM plans on supporting mixed mode allowing some partitions to run in one mode and others to run in the other mode, as well as allowing LE partitions to run under PowerVM.  Please read Jeff Scheel’s blog if you would like to know more about this subject:  https://www.ibm.com/developerworks/community/blogs/fe313521-2e95-46f2-817d-44a4f27eba32/entry/just_the_faqs_about_little_endian?lang=en

“And that brings me nicely to HoP. Is the HANA code recompiled or can it take advantage of some form of emulation? ”

One of the key attributes of HANA is its incredible performance.  As such, even if it were possible to run with emulation, it would defeat the purpose of HANA to run in any sort of degraded mode. One of the ways that HANA delivers its speed is through the use of SIMD, (Single Instruction Multiple Data – http://www.saphana.com/community/blogs/blog/2014/03/19/hana-meets-the-sims-simd-simplicity-and-simulation).  On the Intel platform, SIMD is called by the SSE instruction set and is a single pipeline vector unit within each processor core.  IBM offers a similar vector unit within each of the Power cores, called Altivec, and which now supports dual pipeline vector operations.  Each type of unit is utilized by HANA in the same way, but requires platform specific code.  As such, emulation would not allow SSE based code to work even in emulation mode on an Alitvec based system.  HANA was originally coded for SSE based operations in LE mode on the Intel platform. SAP has modified their code to support Altivec based operations in BE mode on the Power platform which was subsequently compiled to run on the Power platform under PowerVM natively.

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October 2, 2014 - Posted by | Uncategorized

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