It's recently been a year since I started working on my pet OS project, and I often end up looking backwards at what I have done, wondering what made things difficult in the beginning. One of my conclusions is that while there's a lot of documentation on OS development from a technical point of view, more should be written about the project management aspect of it. Namely, how to go from a blurry "I want to code an OS" vision to either a precise vision of what you want to achieve, or the decision to stop following this path before you hit a wall. This article series aims at putting those interested in hobby OS development on the right track, while keeping this aspect of things in mind.
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Member since:2011-01-28
"Second reason why early optimization is bad is that, as I mentioned earlier, there's a degree of optimization past which code becomes dirtier and harder to debug."
Re-writing code in assembly (for example) is usually a bad idea even after everything is working, surely it's even worse to do before. But then this isn't the sort of optimization I'm referring to at all.
Blanket statements like "premature optimization is the root of all evil" put people in the mindset that it's ok to defer consideration of efficiency in the initial design. The important factors proposed are ease of use, manageability, etc. Optimization and efficiency should only be tackled on at the end.
However, some designs are inherently more optimal than others, and switching designs mid stream in order to address efficiency issues can involve a great deal more difficultly than had the issues been addressed up front.
For a realistic example, see how many unix client/server apps start by forking each client. This design, while easy to implement up front, tends to perform rather poorly. So now we have to add incremental optimizations such as preforking and adding IPC, then we have to support multiple clients per process, etc.
After all this work, the simple app + optimizations end up being more convoluted than an more "complicated" solution would have been in the first place.
The Apache project is a great example of where this has happened.
The linux kernel has also made some choices up front which has made optimization extremely difficult. One such choice has been the dependence on kernel threads in the filesystem IO layer. The cement has long dried on this one. Every single file IO request requires a kernel thread to block for the duration of IO. Not only has this design been responsible numerous lock ups for network file systems due to it being very difficult to cancel threads safely, but it has impeded the development of efficient asynchronous IO in user space.
Had I been involved in the development of the Linux IO subsystem in the beginning, the kernel would have used async IO internally from the get go. We cannot get there from here today without rewriting all the filesystem drivers.
The point being, sometimes it is better to go with a slightly more complicated model up front inorder to head off complicated optimizations at the end.
Edited 2011-01-30 22:36 UTC
Member since:2010-03-08
However, some designs are inherently more optimal than others, and switching designs mid stream in order to address efficiency issues can involve a great deal more difficultly than had the issues been addressed up front.
For a realistic example, see how many unix client/server apps start by forking each client. This design, while easy to implement up front, tends to perform rather poorly. So now we have to add incremental optimizations such as preforking and adding IPC, then we have to support multiple clients per process, etc.
Actually, I think this whole fork() thing started as a memory usage optimization. On systems with a few kilobytes of memory like the ones which UNIX was designed to support, being able to have two processes using basically the same binary image was a very valuable asset, no matter the cost in other areas.
Nowadays, however, even cellphones have enough RAM for the fork() system to be a waste of CPU time and coding efforts (hence the decision of the Symbian team not to include it a while ago). But due to legacy reasons and its mathematical elegance, it still remains.
The Apache project is a great example of where this has happened.
All hail the tragedy of legacy code which sees its original design decisions becoming irrelevant as time passes (the way I see it).
I think that should we look deeper, we'd find legacy reasons too. After all, as Linux was designed as a clone of ye olde UNIX, maybe it had to behave in the same way on the inside for optimal application compatibility too ? Asynchronous IO is, like microkernels, a relatively recent trend, which has only be made possible due to computers becoming sufficiently powerful to largely afford the extra IPC cost.
Edited 2011-01-31 07:42 UTC
The Verge pointed me to a blog post by Leap Motion - which reveals how their Kinect-like motion control works with Windows 8. "From the second you plug in your Leap Motion Controller, you'll be able to browse the web and interact with your computer just by moving your hands and fingers in the air. With Leap Motion technology and Windows, you can do everything that's possible with multi-touch inputs - without actually touching anything. This also means that existing applications in Windows 7 and 8 will respond to your natural hand and finger movements. Soon, we'll show you how Leap Motion will work with Mac OS X." Quite cool.
PocketNow interviews Marc Dillon, and there's an interesting note about why Jolla is keeping the display properties under wraps: "We're leaving some of those details out because we do understand that there are a lot of really big players in the market and they tend to take certain components in the market and dominate them. We created the ability to actually be able to run Sailfish on multiple hardware displays and be able to swap components, so this is part of the demand and supply planning phase. We are committed to this industrial design which is a 4.5-inch display, an 8 megapixel camera on the back and a front-facing camera at the front, and the exact specs of the display we'll provide when we're close to delivery." Something you rarely hear anything about.
"This is my NeXTstation Turbo Color booting the Mac System 7.1 Operating System using a hardware add-on called 'Daydream'. The Daydream has a Mac ROM and a few custom ICs in it and hooked up to the NeXTs DSP port. Turns your NeXT into a full fledged 68k powered Mac." So cool.
"The NetBSD Project is pleased to announce NetBSD 6.1, the first feature update of the NetBSD 6 release branch. It represents a selected subset of fixes deemed important for security or stability reasons, as well as new features and enhancements. Please note that all fixes in the prior security/bugfix updates (NetBSD 6.0.1 and 6.0.2) are also in 6.1."
"At the end of a week in which Electronic Arts confirmed it wasn't developing a thing for the Wii U, one of the software engineers in EA Sports' Canada studio, in a series of since-deleted tweets, disparaged the console as 'crap' and suggested Nintendo should give up on hardware altogether. 'The Wii U is crap. Less powerful than an Xbox 360. Poor online/store. Weird tablet', tweeted Bob Summerwill, listed as a senior software engineer at EA Canada, in a reply to a tweet posting a link about EA's no-Wii U news. 'Nintendo are walking dead at this point'." The Wii U is turning into the 21st century's Virtual Boy.
"In NixOS, the entire operating system - the kernel, applications, system packages, configuration files, and so on - is built by the Nix package manager from a description in a purely functional build language. The fact that it's purely functional essentially means that building a new configuration cannot overwrite previous configurations. Most of the other features follow from this." Interesting approach. A Linux distribution, sure, but with some very refreshing ideas about system configuration.
Appfour added, among other features, C/C++ support to its new version of AIDE. From Android-IDE, "Now you can write parts of your app or your whole app in C/C++ on your device. AIDE supports the Standard Android NDK toolchain (GCC 4.6 + Bionic, STL, ...). No changes are necessary if you want to build an app developed on a PC with Eclipse. C/C++ development is fully integrated: Build errors appear in the error list and files can easily be navigated to with Go to file. The editor supports C/C++ syntax highlighting."
Ars nails it: "The answer is that Google did announce what amounts to a fairly substantial Android update yesterday. They simply did it without adding to the update fragmentation problems that continue to plague the platform. By focusing on these changes and not the apparently-waiting-in-the-wings update to the core software, Google is showing us one of the ways in which it's trying to fix the update problem."
"It is good for programmers to understand what goes on inside a processor. The CPU is at the heart of our career. What goes on inside the CPU? How long does it take for one instruction to run? What does it mean when a new CPU has a 12-stage pipeline, or 18-stage pipeline, or even a 'deep' 31-stage pipeline? Programs generally treat the CPU as a black box. Instructions go into the box in order, instructions come out of the box in order, and some processing magic happens inside. As a programmer, it is useful to learn what happens inside the box. This is especially true if you will be working on tasks like program optimization. If you don't know what is going on inside the CPU, how can you optimize for it? This article is about what goes on inside the x86 processor's deep pipeline."
"It was the only moment I heard regret slip into Otellini's voice during the several hours of conversations I had with him. 'The lesson I took away from that was, while we like to speak with data around here, so many times in my career I've ended up making decisions with my gut, and I should have followed my gut,' he said. 'My gut told me to say yes.'" The world would've been a much different place - Apple would have been less dependant on Samsung for its chips, which probably would've meant less money for Samsung to develop its Galaxy business.
Member since:
2010-03-08
That's not what I said, but you must have encountered one of the earlier, less clear edits of my post.
I do not advocate the absolute lack of software optimization which we have nowadays. Though I think feature bloat and poor design are more to blame there, as an aside.
What I advocate is only not optimizing too much too early.
There are several reasons for this.
First, it's a great way to lose time you could have spent on optimizing something more important. Tanenbaum tells us an interesting story in Modern Operating Systems, for that matter : one of his students, who worked on MINIX, spent 6 months optimizing the "mkfs" program, which writes a filesystem on a freshly formatted disk, and more months debugging the optimized version in order to make it work.
This program is generally called exactly once in the life of the operating system, so was it really worth the effort ? Shouldn't he have cut his optimizer's teeth on something more important, like say boot times ?
Second reason why early optimization is bad is that, as I mentioned earlier, there's a degree of optimization past which code becomes dirtier and harder to debug. Caching is a good example. Clean code is very, very important, because past a certain degree of dirtiness one can do nothing with code. Not even optimizing. So this is a though decision, one that is not trivial and which should only be made after profiling has shown that the code is actually too slow as is.