Gordon Monro —Notes

There Is No Free Lunch in the Jungle

Gordon Monro, April 2012

Recently I came across two articles by Herb Sutter, entitled "The Free Lunch Is Over", from 2004 (http://www.gotw.ca/publications/concurrency-ddj.htm), and "Welcome to the Jungle", from 2011 (http://herbsutter.com/welcome-to-the-jungle). Together they chart fundamental changes in the way that computer hardware is organised, and the effect that this is having on computer programs and computer programmers. Sutter is a programming guru who works for Microsoft, and he is particularly interested in changes to programming techniques.

Click to reveal textThe free lunch is over

In "The Free Lunch Is Over", Sutter presciently pointed out that the era of ever faster and more powerful computer processors is ending. The free lunch was the continual increase in computer processor speeds, sustained over a very long period (Sutter says roughly 1975 to 2005, but 1975 is an approximate starting date for desktop computers; for bigger computers it surely extends further back). This meant that software developers didn't have to worry too much about inefficient software; it might be a bit slow today, but tomorrow's machines will run it fast enough. Sutter's article, which first appeared in 2004, pointed out that processor clock speed had started to level out. Since then, there has been almost no increase in clock speed, which has stagnated at something under 4 gigahertz; the obstacle is the amount of heat generated in the small space of the chip. Sutter's first era is the era of the free lunch of ever-increasing processor speeds.

It is still possible to pack ever more transistors into a chip, so since 2005 there has been a proliferation of multi-core chips, where each "core" is equivalent to the whole processor of an earlier machine. Today typical desk-top machines have four cores, and even phones and tablets are beginning to have two cores. Different programs can run at the same time on different cores, but to really make use of the cores a single program has to utilise several cores simultaneously. This requires a big change on the part of programmers, who need to acquire new tools and a new mindset. Various approaches to what is variously called parallel programming, concurrency or multi-threading have been around for a long time, but now they suddenly become central. Sutter's second era is "multi-core", that of machines with a relatively small number of powerful cores. The first article takes us to this point.

Click to reveal textWelcome to the jungle

In the second article "Welcome to the jungle", Sutter considers that the "multi-core" era is already ending even before we have learnt to cope with it. The third era is that of "hetero-core", the era of heterogeneous cores, which according to Sutter started in 2011. As far as the actual hardware is concerned, the third era arrived when powerful graphics cards started to be fitted to home computers for computer games. These graphics cards contain a large number (for example 100) of very small specialised cores, originally only capable of processing pixels for display. These small cores have gradually become more general-purpose, and there has been considerable interest in scientific computing circles in harnessing their power for general-purpose computation, not just graphics. This interest is now going mainstream, but it brings with yet more challenges for programmers, as now, added to the already difficult challenge of adapting a program to make use of multiple cores, different parts of the one program may be running on cores with very different capabilities.

Sutter has the "hetero-core" era ending some time in the 2020s because he thinks that is when Moore's Law (that the number of transistors on a chip doubles every two years) will finally end. At that point our desktop and laptop and pocket computing devices will have as much power as they are going to get. Sutter thinks by then another trend will have already taken over, the availability of "hardware as a service": enormous clusters of computers available to be used over the Internet by anyone, for a fee. This provides still another challenge for programmers: a program will run partly on the by then 1,000 or more heterogeneous cores in the user's local machine (desktop, laptop, tablet or phone), and partly on a much bigger collection of cores available at the other end of a wi-fi link. Sutter considers that building larger and larger networks of computers will be, for the foreseeable future, much easier than cramming more and more transistors into a single chip or box, so growth in computing power will take place less in individual machines and more in the availability of networks of computers. As Sutter points out, already Amazon and others offer large clusters of computers for hire; he gives the example of a cluster with 30,000 virtual cores that was (virtually) put together for a pharmaceutical company who hired it for one day, at a cost of under $1500 per hour. The calculations would have taken years on a desktop computer.

Interesting times!

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