| Meet the new Linux kernel: 2.6.21 |
Apr. 26, 2007
It took longer than Linux creator Linus Torvalds would have liked, but the latest Linux kernel, version 2.6.21, has arrived. It brings many minor and major changes in how Linux handles process scheduling and time.
In his April 25th release note to the LKML (Linux Kernel Mailing List), Torvalds wrote, "If the goal for 2.6.20 was to be a stable release (and it was), the goal for 2.6.21 is to have just survived the big timer-related changes and some of the other surprises."
Surviving all those changes took time. "It's been over two and a half months, and while it's certainly not the longest release cycle ever, it still dragged out a bit longer than I'd have hoped for and it should have."
The delays came in large part because of "all the timer changes to support a tickless system (and even with ticks, more varied time sources)." Torvalds called timer-related improvements "the big change during 2.6.21."
A tickless system you ask? In 2.6.21, new technologies called clockevents and dyntick (dynamic ticks) were introduced. The technologies are based on previous real-time Linux work by Ingo Molnar and Thomas Gleixner. Together, they make the new kernel more efficient, both in terms of saving power, and in terms of dealing with heavy-duty multi-tasking jobs such as virtualization.
The clockevents feature provides a uniform interface and a device API for a computer's various timekeeping and scheduling devices. With this, developers don't need to delve down to the hardware level to work with a computer's timing mechanisms, making it much easier to program extremely accurate timekeeping.
The other new feature, dynticks, saves power by shutting down the system clock more completely during periods of idleness. It works like this.
With earlier kernels, the system clock keeps "ticking" the timer interrupt even when the system has gone idle, at a rate of 1,000 ticks per second, or 1 KHz. That wastes a lot of Watts when the CPU is doing nothing but virtually twiddling its thumbs waiting for another job.
With Dynticks, the timer interrupt is turned almost off and the CPU waits for a real interrupt to come from a program, network interface, or the like. By idling your processor, you save energy -- and on a laptop, that's not a small matter.
In the future, both these features will be used to improve virtualization. The virtualization manager -- rather than scheduling by HZ -- will determine which program or virtual operating system should have the lion's share of the processor's time. This is not a pie in the sky idea. The technique was already being used with Linux on IBM mainframes years ago, when trying to deal with a thousand virtual Linux servers at once using HZ scheduling. It lead to situations where the timer interrupt overhead alone was using up almost all of the processors' time.
While no one is likely to be running that many Linux virtual machines anytime soon on typical x86 server hardware, the new Linux kernel does also feature many improvements to the VMI (Virtual Machine Interface) and KVM (Kernel Virtual Machine). With the former, a better interface for paravirtualization programs like Xen and VMWare has been introduced. In the later case, major improvements have been made to KVM 15, the hardware-based virtualization program that was introduced in Linux 2.6.20.
There were also numerous minor improvements. Some of the most significant of these were in the fields of network and audio device support.
One feature that was not included in 2.6.21 is the Reiser4 file system. For years now, it's been a major issue in developer circles whether this innovative and fast file system would become part of the Linux kernel.
When its designer and developer Hans Reiser was arrested for the murder of his wife in October 2006, it was assumed that development would stop on his file system and that would be the end of any chance of it being adopted by mainstream Linux.
It turns out that Reiser4 is still being maintained by programmers at Reiser's company, Namesys, and that there is still interest in having the file system in Linux. In a LKML note, Andrew Morton, the production Linux kernel maintainer, wrote that the problem with getting Reiser into Linux isn't Reiser's developers. "That's not where the problem lies -- the Namesys guys are responsive and play well with others."
While Morton hasn't "looked at the reiser4 code in ages," he doesn't see "anything like a list of outstanding technical issues." So Morton suggests that "to get it unstuck we'd need a general push; get people looking at and testing the code; get the vendors to have a serious think about it, etc. We could do that -- it'd require that the Namesys people (and I) start making threatening noises about merging it, I guess."
So, it could turn out that the big news in the next version of Linux may be the adoption of the Reiser4 file system. Failing that, you can expect to see more "tickless" and virtualization improvements in Linux's continuing evolution.
-- Steven J. Vaughan-Nichols
Do you have comments on this story?
Talkback here
NOTE: Please post your comments regarding our articles using the above link. Be sure to use this article's title as the "Subject" in your posts. Before you create a new thread, please check to see if a discussion thread is already running on the article you plan to comment on. Thanks!
(Click here for further information)
|
|
|
7 Advantages of D2D Backup
For decades, tape has been the backup medium of choice. But, now, disk-to-disk (D2D) backup is gaining in favor. Learn why you should make the move in this whitepaper.
4 Legal Reasons to Control Internet Access
The Internet is obviously a valuable resource for many organizations. However, many are exposed to legal liability concerns because they fail to control Internet access. Learn if you're safe in this white paper.
Rapidly Resolve J2EE Application Problems
Whether you are in the process of building J2EE applications or have J2EE applications already running in production, you must ensure that they deliver the expected ROI. Learn how in this white paper.
Load Testing 2.0 for Web 2.0
There are many unknowns in stress testing Web 2.0 applications. Find out how to test the performance of Web 2.0 in this white paper.
Build Better Games Online
For the game infrastructure providers, life is complex. Making money from games has become more complicated. Why? Find out in this white paper.
Building a Virtual Infrastructure from Servers to Storage
This white paper discusses the virtual storage solutions that reduce cost, increase storage utilization, and address the challenges of backing up and restoring Server environments.
Gaining Faster Wireless Connections with WiMAX
Welcome to what is quickly becoming the hyperconnected world where anything that would benefit from being connected to the network will be connected. Learn more in this white paper.
Is Your Desktop a Security Threat?
The new wave of sophisticated crimeware not only targets specific companies, but also targets desktops and laptops as backdoor entryways into those business’ operations and resources. Learn how to stay safe in this white paper.
Increasing SAN Reliability by 100 Percent
Storage area networks (SAN) are a strong part of storage plans. Learn how to increase your reliability and uptime by 100 percent in this case study.
|
|
|
|
|
Use of this site is governed by our Terms of
Service and Privacy Policy.
Except where otherwise specified, the contents of this site are copyright © 1999-2008
Ziff Davis Enterprise Holdings Inc. All Rights Reserved.
Reproduction in whole or in part in any form or medium without express written permission of Ziff Davis Enterprise is
prohibited. Linux is a registered trademark of Linus Torvalds. All other marks are the property of their respective owners.
news feed