If you wish to get every possible millisecond out of your system, there are a few things you should know about directories in UNIX file systems. (Though technically I'm talking about the implementation of the EXT2 file system, the points apply to almost all UNIX file systems.)
First note that though the command ls always displays the directory in a sorted order, directories are not stored with their entries sorted. Instead, each new entry is placed as close to the front of the directory as possible.
To find a file in a directory, the file name is compared with the first file in the directory. If it doesn't match, the second name is checked, and so on until either a match is found, or the end of the directory is reached. Consequently, if you have a large number of files in a directory and are frequently opening the last file in the directory, your CPU is doing a lot of comparisons. If, however, you could control the order of the entries, so as to place the most-frequently-used entries at the beginning of the directory, this would not be such an issue.
If you want to redo the internal ordering of the entries in /dev, boot from a floppy and then mount your primary file system. If your regular file system is mounted as /mnt, your regular device directory is /mnt/dev. Create a new directory called /mnt/dev2. Now you can move device files from /mnt/dev to /mnt/dev2. You will probably want to start with /mnt/dev/zero and /mnt/dev/null, as these two are opened far more frequently than any other devices.
If that sounds like a hassle, then don't bother with it. You probably won't notice any difference unless you are running on an old 386. Furthermore, the new directory cache under development in the 2.1.x kernel series will most likely make this a non-issue.
Preston Crow grew up in Boise, Idaho. He has a Master's degree in Computer Science from Dartmouth College and hopes to soon upgrade to a Ph.D. He now works for the Open Group in Cambridge, MA, where he lives with his brilliant wife. He can be reached via e-mail at Preston.F.Crow@Dartmouth.edu.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide