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Comment: Re:Linux kernel is mostly 80-column (Score 1) 330

by Mr Z (#48446465) Attached to: Eizo Debuts Monitor With 1:1 Aspect Ratio

Yep, I'm with you here.

I did a stint with 132 columns awhile back (back when I was running Linux on a machine that wasn't quite powerful enough to run X11), and I found the extra horizontal space to be mostly wasted. If I did start putting comments or code over there, it'd often get "lost".

Now, I do use a wide format for certain debugging applications. It also works well for spreadsheets. But for source code? I've definitely got an 80 column mind, despite ever having used punch cards or paper tape. I went from 28 columns to 40 to 80 as I learned programming in the 1980s. 80 columns is a very comfortable width. 132 pushed it too far.

80 columns actually corresponds pretty well to the amount of text you'd have on a type-written page on standard letter size paper (or A4, if you prefer). You get 60 to 72 characters across (assuming 1" margins) depending on whether you're 10CPI or 12CPI, and that's roughly how wide programs are when written within 80 column boundaries.

Comment: Re:Lamport (Score 2) 42

by Mr Z (#48385473) Attached to: Google Quadruples A.M. Turing Award To $1M


A few years back, I was implementing Leslie's Bakery Algorithm. (Which, to be sure, you should look up his original paper, not the bastardizations you sometimes find in textbooks. That paper and more are available here.)

In my implementation, I wanted to SIMD-ize one of the steps to make it more efficient. I thought the transformation was valid, but wasn't certain, so I emailed Dr. Lamport. I was pleasantly surprised when Leslie actually replied to my email.

And yes, the transformation was valid. *whew* Our multiprocessor DSP software got a little faster that day.

Anyway, there's some fascinating stuff on his page full of papers. The link again: http://research.microsoft.com/en-us/um/people/lamport/pubs/pubs.html

Comment: Re:Hyperbolic headlines strike again (Score 1) 181

by Mr Z (#48357171) Attached to: There's No Such Thing As a General-Purpose Processor

I think part of the problem is that the axes aren't linear. If you know the problem you're trying to tackle a priori you can tackle it with multiple magnitudes of greater efficiency. For a fully specified, unchanging problem, I'd expect 3 orders of magnitude or better in most spaces, because you'd build exactly the hardware you need, and strip away all the hardware that supports unneeded programmability—you build a hardwired ASIC. Even in the programmable space, spending a bit of effort matching your problem to your processor can bring huge gains in efficiency, at least 5x. Also, consider that efficiency isn't just run time, but rather a function of power, performance, and cost.

The algorithms that run on a hearing aid would sop the hearing aid's battery before they were even fully loaded if you tried to run them on a typical desktop processor. But, they're baked down to a hyperefficient DSP or ASIC that's tuned specifically for the problem.

You cite a SPEC benchmark that runs faster on an A7 than an A15. Is that in clocks or wall-clock time? I suspect it's dominated by pointer dereferences, such as a linked list traversal. Load-to-use latency (which isn't a function of cache organization, but rather pipeline depth) becomes a dominant term for those workloads.

Backing up a bit: My problem with your thesis is that you assume there's a "best GPP" and then seek to prove there's no one processor that could possibly be that on the basis that across random applications, the winner varies. Your argument seems to be, at the limit: "if you don't tell me your application ahead of time, I can't pick a best processor, so therefore there's no general purpose processors."

It's the other way around. There's a cluster of processors that are OK at a range of random tasks. They're distinguished from special-purpose processors by the fact that the special purpose processor performs at least 5x or more (and likely orders of magnitude in some cases) better than the average for the cluster. That's true even if some of the processors in that cluster are 2x more efficient than the others. A processor is a GPP if there's few or no problems for which it's orders of magnitude more efficient than its cohort. 2x is nothing to sneeze at, but a specialized processor should reach much higher. 5x at a minimum.

And please note I'm mentioning efficiency. It's not raw cycles or even wall clock time. Maybe a better measure is "energy per function", or "energy per function per dollar." (Although the latter is a bit dubious, as you buy the hardware once, but you use it many, many times. Lifetime costs are best approximated by energy costs over the lifetime of the device, if you're doing significant compute.)

You mention GPUs. Sure, GPUs provide cheap FLOPs, and they can even start to run arbitrary C programs. But, what %age of those FLOPs get utilized when running random programs? You might get a 4x speedup offloading some algorithm to your video card, but is that a win when your video card's raw compute power is 100x your host CPUs? Would you buy a Windows machine powered only by a GPU, running everything from your statistical regression to your web browser?

(I may exaggerate, but only slightly.)

To me, "general purpose" means, "I run the compiler, and for the most part, I get what I get. If there's some hotspots, maybe I can tune for this specific architecture. Most of the time, I don't worry." Specialized means "by selecting this processor for this task, I know up front I need to spend time optimizing the implementation of the task to this processor."

Perhaps the qualm is that really that's more a function of the application than the processor. OK. I can buy that. But, when you look across the space of processors that get deployed in that way, you'll see that most processors tend to end up one one side or the other of that line fairly often, and few are on the fence. You find very few DSPs and GPUs asked to run Linux or Windows kernels and applications (the core code, not the stuff they compile to be offloaded, say, in a shader language). You find some number of x86s asked to run signal processing applications, but only where they can afford the cooling.

Comment: Re:Mind-blowingly cool, but... I don't get it. (Score 1) 79

by Mr Z (#48328087) Attached to: First Experimental Demonstration of a Trapped Rainbow Using Silicon

Due to self-interference, the light bumps into itself on the way out, and subsequently can't get out. At least at my limited level of understanding, it's the wave-light nature of light at play here.

I imagine at some point, the trapped photons all get absorbed and the original energy dissipates as heat.

Comment: Re:Also which languages that beginners choose. (Score 1) 217

by Mr Z (#48317813) Attached to: The Effect of Programming Language On Software Quality

FWIW, I technically had some C++ before Perl, but not enough that I count it.

Re: Perl: I'm much the same way with Perl. I use Perl for lots of quickie projects. Great for anything I'm only going to spend at most a couple days developing.

Perl's also great for much larger projects too, where runtime performance isn't absolutely critical but flexibility and development ease is paramount. We actually have some fairly significant projects at work that are written in Perl.

One of them, which embeds Perl in another language as a metaprogramming language. I couldn't imagine trying to write that in C++ without a dedicated team. But, a set of hardware designers are effectively maintaining the tool in the background thanks to it being written in Perl.

Comment: Re:Also which languages that beginners choose. (Score 3, Interesting) 217

by Mr Z (#48317403) Attached to: The Effect of Programming Language On Software Quality

As for which language is your gateway language, it probably depends on what era you started programming in, too. My path was Microsoft BASIC => Assembly => Turbo Pascal => C => Perl => C++11, with some shell scripting and other goodies around the fringes. I've probably written more C than anything, but C++11 rules my future. Turbo Pascal was my short-lived gateway to C, where I then spent most of my career. I wrote some truly regrettable neophyte-programmer code in C there at the beginning, so really C was where I grew from a college-aged hacker to someone who can actually program. Now guess how old I am. ;-)

I guess for an analysis like this, you really need to limit yourself to people who consider themselves competent programmers. Those VB macro whizzes in accounting likely consider themselves accountants, not programmers. Likewise for the physicist with a pile of creaky MATLAB models.

BTW, I have to agree with you 100% on make and bash. I consider myself above average on make as compared to my coworkers, but that's an extremely low bar. And while I've done some crazy stuff in bash in the past, these days I'll hop over to perl for anything more than 10 - 20 lines, especially if I find too much 'sed' showing up or find myself wanting an actual data structure.

Comment: Re:Take away for me (Score 4, Interesting) 217

by Mr Z (#48317317) Attached to: The Effect of Programming Language On Software Quality

I finally brought up the PDF. It appears the authors consider C++ weakly typed because it allows type-casting between, say, pointers and integers.

While this is strictly true, I find myself avoiding such things whenever possible. Main exception: When talking directly to hardware, it's often quite necessary to treat pointers as integers and vice versa.

I guess to fairly evaluate a language like C++, you need to categorize programs based on how the language was used in the program. If you stick to standard containers and standard algorithms, eschewing casting magic except as needed (and using runtime-checked casts the few places they are), your program is very different than one that, say, uses union-magic and type punning and so on every chance it gets. (I've written both types of programs... again, FORTRAN in any language.)

One of my more recent projects was written ground-up in C++11. It relies on type safety, standard containers, standard algorithms, smart pointers (shared_ptr, unique_ptr) fairly heavily. It's been quite a different experience to program vs. my years of C programming. Way fewer dangling pointers, use-after-free errors, off-by-one looping errors, etc. But, the paper lumps both languages into the same bucket. That hardly seems fair.

Comment: Re:Take away for me (Score 3, Interesting) 217

by Mr Z (#48317033) Attached to: The Effect of Programming Language On Software Quality

I wonder if you can do an analysis of code bases across languages for the same team? I regularly write significant amounts of C++ (these days, C++11), Perl and assembly language. Those are three rather different languages, with strong, weak and largely non-existent type systems, respectively.

Of course, all three languages also open themselves to a wide range of programming styles, and I imagine if you picked any other set of languages you could make a similar statement. But if you measure the same programmers programming in across them (assuming a reasonably high level of proficiency in all of them), then perhaps you can determine what portion of the effect is due to the programmer vs. due to the language.

After all, Real Programmers can write FORTRAN in any language.


Microsoft Works On Windows For ARM-Based Servers 113

Posted by timothy
from the arms-race dept.
