IBM Systems Magazine, Mainframe - November/December 2016 - L12


can immediately do some work,
allowing you to get more out
of the core.
On the z13*, our latest
machine, each of the cores can
split into two so-called hardware
threads. OS tasks can be loaded
on one of those threads. To the
OS, these hardware threads look
exactly like a logical CPU, so the
OS knows how to deal with it.
The two logical CPUs share the
hardware resources of the core. If
both of them are running at the
same time, they share to such an
extent that each of the hardware
threads will be slower than a single task running on the core. But
in combination, they are faster.
That's the goal of MT. A machine
can have multiple cores, and
each of the cores has two CPUs
defined and can run two things
on each core.
ISM: Do all workloads benefit
from MT?
MS: We recommend that our
clients test their workloads with
and without MT. The best thing
to do is try MT on your system.
Throw the workload on the
machine with and without MT to
see what happens.
One general rule to help determine if a workload would benefit
from MT is underutilization of
the processor resources when
running a single task. A second
thread can then fill the gaps left
by the first thread.
Negative indicators also
exist. If some core resources
are sparse, MT won't benefit
the workload. For example,
if one thread needs all of the
translation lookaside buffers,
loading two threads on the core
will cause fights over resources.
Poor scaling of the application
is the biggest negative indicator,
as adding MT will only make the
situation worse.

ISM: What are extended Berkeley Packet Filter (eBPF)
and non-uniform memory access (NUMA) emulation for
kernel-based VM (KVM)? How do they benefit clients?
MS: The original BPF was a simple language
interpreted by the kernel that was limited to 32bit registers and a small set of instructions. The
concept is found on a lot of UNIX-like OSes and was
originally used to filter networking packets.
eBPF is the latest version of BPF. It has 64-bit
registers and a few more instructions to make it
more versatile. The eBPF program returns a yes or
no answer to a data query, and you can use it for all
kinds of filtering. The IT community has started to
find new use cases for the eBPF, such as trace-event
filtering, which uses trace points in the kernel to
find performance problems.
Even more interesting is system-call filtering
where a BPF program is used to filter the system
calls issued by a user program. This is interesting
for Docker. You can use system-call filtering based
on eBPF to limit what your Docker image can do.
NUMA emulation is a tool for system scaling for
very large systems-particularly if you're running
a KVM host. A large system can have up to 10 TB
of memory and 141 cores. With such a system,
a single memory node is used by all of the CPUs
working in memory management. As a result,
points of contention often exist.
A simple way to ease these problems is to artificially split the memory into multiple nodes. With
NUMA emulation, you can split the memory into
a number of fake nodes (e.g., eight units of 1.25
TB each). The advantage is that some of the data
structures are duplicated. Each of the memory
nodes now has its own set of locks, so the contention points are reduced. Each of the nodes has
a kswap daemon, which is a background process
used for housekeeping that makes sure enough
memory is free. NUMA emulation was invented for

KVM as a host because of the
issues with paging performance.
Our performance analysis shows
NUMA emulation results are
mixed. More work must be done
for the scalability of large systems.
ISM: What advantages do IBM z
clients receive by running Docker?
MS: Docker is a step-up approach
for software development and
rapid application deployment.
You manage images by using a
version control system. If done
right, you have resource sharing
among the Docker instances of
specific images. Overall, you
get a virtual container, which is
something less than a VM.
Docker provides container
management systems for images
and the capability to share these
images with the registry. Docker
looks and feels the same on
Linux on z Systems as it does on
x86, except x86 has more prebuilt images. The advantage of
running Docker on z Systems is
that you're running on the most
reliable hardware.
ISM: Could you talk about the
supported Linux distributions-
Red Hat, SUSE and Ubuntu? What
capabilities do they bring to
z Systems?
MS: Without these distributors,
Linux on z Systems wouldn't
exist because they build things

12 // NOVEMBER 2016 Linux on z Systems

Linux_on_z_1116.indd 12

9/29/16 1:14 PM



Table of Contents for the Digital Edition of IBM Systems Magazine, Mainframe - November/December 2016

Editor's Desk: Mastering their craft
IBM Perspective: Expanding mainframe ecosystem creates opportunities for Gen Z
Partner PoV: Workplace Diversity: Attract the best talent by encouraging more options for women
IT Today: Financial Feasibility: IBM Global Financing designs customized solutions for technology investments
Currents: Giving Data Structure: Find the right database management systems to maximize information
Case Study: Investing in a Difference: Primerica Life Insurance Co. improves processing and performance
Cover Story: Sparking Student Interest: IBM Master the Mainframe World Championship exposes top students to analytics and data storage
Feature: The Modern Mainframer: The IBM z platform attracts recent grads to its orbit
Women in Tech: Taking a Seat at the IT Table: Women meet challenges, savor successes in the IT field
Tech Corner: Get in the Cloud: z/OS solutions can connect to the cloud through REST interfaces
Solutions: API Integration Platform 3.0, OpenLegacy; Ivory Service Architect V5.1, GT Software
Stop Run: Code Your Own Way: High school girls take charge of their futures
Reference Point - Global Events, Education, Resources for Mainframe
Linux on z Systems E-book
2016 Mainframe Solutions Edition Product Index
IBM Systems Magazine, Mainframe - November/December 2016 - Intro
IBM Systems Magazine, Mainframe - November/December 2016 - Cover1
IBM Systems Magazine, Mainframe - November/December 2016 - Cover2
IBM Systems Magazine, Mainframe - November/December 2016 - 1
IBM Systems Magazine, Mainframe - November/December 2016 - 2
IBM Systems Magazine, Mainframe - November/December 2016 - 3
IBM Systems Magazine, Mainframe - November/December 2016 - 4
IBM Systems Magazine, Mainframe - November/December 2016 - 5
IBM Systems Magazine, Mainframe - November/December 2016 - Editor's Desk: Mastering their craft
IBM Systems Magazine, Mainframe - November/December 2016 - 7
IBM Systems Magazine, Mainframe - November/December 2016 - IBM Perspective: Expanding mainframe ecosystem creates opportunities for Gen Z
IBM Systems Magazine, Mainframe - November/December 2016 - Partner PoV: Workplace Diversity: Attract the best talent by encouraging more options for women
IBM Systems Magazine, Mainframe - November/December 2016 - 10
IBM Systems Magazine, Mainframe - November/December 2016 - IT Today: Financial Feasibility: IBM Global Financing designs customized solutions for technology investments
IBM Systems Magazine, Mainframe - November/December 2016 - 12
IBM Systems Magazine, Mainframe - November/December 2016 - 13
IBM Systems Magazine, Mainframe - November/December 2016 - Currents: Giving Data Structure: Find the right database management systems to maximize information
IBM Systems Magazine, Mainframe - November/December 2016 - 15
IBM Systems Magazine, Mainframe - November/December 2016 - 16
IBM Systems Magazine, Mainframe - November/December 2016 - 17
IBM Systems Magazine, Mainframe - November/December 2016 - Case Study: Investing in a Difference: Primerica Life Insurance Co. improves processing and performance
IBM Systems Magazine, Mainframe - November/December 2016 - 19
IBM Systems Magazine, Mainframe - November/December 2016 - 20
IBM Systems Magazine, Mainframe - November/December 2016 - 21
IBM Systems Magazine, Mainframe - November/December 2016 - 22
IBM Systems Magazine, Mainframe - November/December 2016 - 23
IBM Systems Magazine, Mainframe - November/December 2016 - Cover Story: Sparking Student Interest: IBM Master the Mainframe World Championship exposes top students to analytics and data storage
IBM Systems Magazine, Mainframe - November/December 2016 - 25
IBM Systems Magazine, Mainframe - November/December 2016 - 26
IBM Systems Magazine, Mainframe - November/December 2016 - 27
IBM Systems Magazine, Mainframe - November/December 2016 - Feature: The Modern Mainframer: The IBM z platform attracts recent grads to its orbit
IBM Systems Magazine, Mainframe - November/December 2016 - 29
IBM Systems Magazine, Mainframe - November/December 2016 - 30
IBM Systems Magazine, Mainframe - November/December 2016 - 31
IBM Systems Magazine, Mainframe - November/December 2016 - 32
IBM Systems Magazine, Mainframe - November/December 2016 - Women in Tech: Taking a Seat at the IT Table: Women meet challenges, savor successes in the IT field
IBM Systems Magazine, Mainframe - November/December 2016 - 34
IBM Systems Magazine, Mainframe - November/December 2016 - 35
IBM Systems Magazine, Mainframe - November/December 2016 - 36
IBM Systems Magazine, Mainframe - November/December 2016 - 37
IBM Systems Magazine, Mainframe - November/December 2016 - 38
IBM Systems Magazine, Mainframe - November/December 2016 - 39
IBM Systems Magazine, Mainframe - November/December 2016 - 40
IBM Systems Magazine, Mainframe - November/December 2016 - 41
IBM Systems Magazine, Mainframe - November/December 2016 - 42
IBM Systems Magazine, Mainframe - November/December 2016 - 43
IBM Systems Magazine, Mainframe - November/December 2016 - Tech Corner: Get in the Cloud: z/OS solutions can connect to the cloud through REST interfaces
IBM Systems Magazine, Mainframe - November/December 2016 - 45
IBM Systems Magazine, Mainframe - November/December 2016 - 46
IBM Systems Magazine, Mainframe - November/December 2016 - Solutions: API Integration Platform 3.0, OpenLegacy; Ivory Service Architect V5.1, GT Software
IBM Systems Magazine, Mainframe - November/December 2016 - Stop Run: Code Your Own Way: High school girls take charge of their futures
IBM Systems Magazine, Mainframe - November/December 2016 - Cover3
IBM Systems Magazine, Mainframe - November/December 2016 - Cover4
IBM Systems Magazine, Mainframe - November/December 2016 - Reference Point - Global Events, Education, Resources for Mainframe
IBM Systems Magazine, Mainframe - November/December 2016 - RF2
IBM Systems Magazine, Mainframe - November/December 2016 - Linux on z Systems E-book
IBM Systems Magazine, Mainframe - November/December 2016 - L2
IBM Systems Magazine, Mainframe - November/December 2016 - L3
IBM Systems Magazine, Mainframe - November/December 2016 - L4
IBM Systems Magazine, Mainframe - November/December 2016 - L5
IBM Systems Magazine, Mainframe - November/December 2016 - L6
IBM Systems Magazine, Mainframe - November/December 2016 - L7
IBM Systems Magazine, Mainframe - November/December 2016 - L8
IBM Systems Magazine, Mainframe - November/December 2016 - L9
IBM Systems Magazine, Mainframe - November/December 2016 - L10
IBM Systems Magazine, Mainframe - November/December 2016 - L11
IBM Systems Magazine, Mainframe - November/December 2016 - L12
IBM Systems Magazine, Mainframe - November/December 2016 - L13
IBM Systems Magazine, Mainframe - November/December 2016 - L14
IBM Systems Magazine, Mainframe - November/December 2016 - L15
IBM Systems Magazine, Mainframe - November/December 2016 - L16
IBM Systems Magazine, Mainframe - November/December 2016 - L17
IBM Systems Magazine, Mainframe - November/December 2016 - L18
IBM Systems Magazine, Mainframe - November/December 2016 - L19
IBM Systems Magazine, Mainframe - November/December 2016 - L20
IBM Systems Magazine, Mainframe - November/December 2016 - L21
IBM Systems Magazine, Mainframe - November/December 2016 - L22
IBM Systems Magazine, Mainframe - November/December 2016 - L23
IBM Systems Magazine, Mainframe - November/December 2016 - 2016 Mainframe Solutions Edition Product Index
IBM Systems Magazine, Mainframe - November/December 2016 - SE2
IBM Systems Magazine, Mainframe - November/December 2016 - SE3
IBM Systems Magazine, Mainframe - November/December 2016 - SE4
IBM Systems Magazine, Mainframe - November/December 2016 - SE5
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