Friday, May 25, 2007

My Message to Virtualization Vendors

Virtualization is about creating illusions (see Chapter 7 in Guerrilla Capacity Planning). However, vendors need to recognize that virtualization is a double-edged sword.

Constructing illusions by hiding physical information from users is one thing, propagating that illusion to the performance analyst or capacity planner is quite another, and considered harmful.

Presumably, it's also potentially bad for business, in the long run. This unfortunate situation has arisen for one of the following reasons:

  1. The performance data that is available is incorrect.

    Example: Enabling hyperthreading on a Xeon processor misleads the operating system, and thereby performance tools, into treating the single core as 2 virtual processors. This means that many performance management tools will conclude and report that your system has 200% processor capacity available. But, this is an illusion, so you will never see 200% processor capacity.

  2. The correct performance data is not made available.

    Example: With hyperthreading enabled, there should be a separate register or port that allows performance management tools to sample the actual utilization of the single physical core (AKA the execution unit). The IBM Power-5 has something called the PURR register that performs this role.

There are many examples of this kind of mangled performance shenanigans in the virtualized world, especially in what I call the meso-VM (PDF) level such as VMware and XenSource. The good news there is, since it's software, it's easier to modify and therefore more likely that actual performance data will become exposed to the analyst.

In other words:

Fewer bells, more whistles

should be the watchword for virtualization vendors.

Wednesday, May 23, 2007

Greek for Geeks

When we come to discuss queueing models in my training classes, I emphasize the fact that my approach to the subject comes from wanting to avoid the blizzard of Greek (mathematical notation) that usually makes the whole subject so obscure to the very people who could use it most; performance analysts.

More on Moore

In an opinion piece in this month's CMG MeasureIT e-zine, I examine what is possibly going on behind the joint IBM-Intel announcement and the imminent release of 45 nm 'penryn' parts in CMOS.

Some related blog entries are:

Tuesday, May 22, 2007

How to Extend Load Tests with PDQ

Suppose you want to assess the scalability of a web application based on measurements from a test rig using a load-test tool like LR, WAS or Grinder. There's one slight problem. The load-test tools are limited to running a finite number (N) of client-side load generators, and that number will always be much much smaller than the number of actual web users submitting transactions when the application goes live. How can you bridge that gap?

Saturday, May 5, 2007

ORACLE Scalability Oracles

For those of you concerned with ORACLE 10g performance, there are a couple of books by ORACLE oracles that you might find useful; especially with regard to ORACLE scalability

Tuesday, May 1, 2007

Programming Multicores Ain't Easy

MIT researchers are exploring a way to make parallel programming easier in order to take full advantage of the computing potential available in multicore-based computers. Many experts believe that unless parallel programming is made easier, computing progress will stall. I discussed this point in my CMG 2006 paper (download PDF).

In single core systems, software code basically runs sequentially, with each task occurring one after another, but in multicore systems tasks get split up among the cores and when different tasks need to access the same piece of memory and fail to properly synchronize the data can become corrupted and cause the program to crash. MIT has designed StreamIt, a computer language and a compiler that basically hides parallel-programming challenges but also allows for full use of multicore processors.