Power Linux is Special

December 5th, 2018

Ron Gordon
Director » Power Systems

I recently read a blog that said Linux is Linux is Linux, and that one should not look at Linux distributions on IBM Power Systems as anything special or different.

Well, I certainly take exception to that premise.

First, let me state that in fairness to other blogs, from an application development and execution standpoint, the Linux distributions for IBM Power are equivalent to other architectures, such as x86. Every IBM Power Systems server runs Linux and is supported by distributions from Red Hat, SUSE, Ubuntu and now Centos and Debian. With the Power Systems Little Endian support on POWER8 and POWER9 systems, there is true application compatibility, as long as the applications are LSB compliant and do not exploit any irregular ABIs, based on deep architectural differences. And, for sure, most all JAVA and interpretive scripting is compatible, from an application standpoint.

But, to say Linux is Linux is Linux ignores the point that system architectures are different . The Linux kernel is aware of these differences and exploits them to provide specialized architectural support, which can result in significant reliability, performance, and capacity differences when choosing the best system to support the needs of a particular application. Server choice is a basic tenant of Linux. Running a firewall has very different system requirements than running mission critical databases and AI, for example.

In the Linux kernel, there is a section of the 2.4 million lines of code that is for architecturally-unique exploitation. In POWER, this section contains code that exploits virtual memory management (as the TLBs and tables are in the hypervisor and not in the OS); reliability and retry features not found in x86 systems; SMT8 for performance; PowerVM support for enhanced virtualization capabilities over VMware, HyperV and KVM; and large memory support. When the kernel is compiled into an operating system for IBM Power Systems, the support is included to provide these performance and mission critical factors. These capabilities are unique to Power Systems and are not found in x86 architectures.

In x86 architectures, while there may be differences base on various system providers (eg, Dell, Lenovo, HP, etc.), there is only one x86 architecture section, so that any advanced functions added by vendors will not be exploited. Hence, the x86 systems are all Linux is Linux is Linux, which brings up another point.

Most Linux distributors have a single build stream for ease of development and support. As such, the x86 build stream is the preferred build. This sometimes inhibits IBM Power Systems since some of the performance characteristics are set in the x86 architecture, which is not optimized for Power Systems. Items, such as Java garage collection cycles, IO block sizes, IO schedulers, etc., should be reviewed and possibly modified by Linux on Power users for optimal performance.

And, I have one more point related to Linux on Power. Due to the very nature of IBM Power Systems, normally, the install procedure of Linux on Power is slightly different than the install on x86 systems.

So, in my opinion, while I do recognize that Linux is consistent in application development and execution, I further contend that Linux is not always the same as you move between system architectures. Without the Linux architectural optimizations, Linux would be reduced to supporting the least common denominator of systems which would eliminate systems architectural differences.

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