Thoughts by Ted

Musings about Open Source, Linux, and Life by Theodore Tso

Archive for October, 2007


Tip ‘o the hat, wag o’ the finger — Linux power savings for laptop users

Published October 29th, 2007 in Linux, OSS | 26 Comments »

It’s interesting to see how far, and yet how much more work we need to do on power management for Linux. I recently got a new laptop — a Lenovo Thinkpad X61s — and using the powertop tool, I was able to configure my system to the point where in what I can “airplane mail reading mode” (mailbox preloaded into memory, USB disabled, wireless and ethernet disabled, backlight down to 30% brightness, sloppily written power hogs like Firefox and Notes — every single application writer should be forced to run powertap and explain why their program feels it necessary to constantly wake up the CPU), I can get my usage down to about 9.8 watts. Using the 8 hours extended battery, that’s 8 hours of battery life, although granted doing very little. On the flip side, if I’m doing a major kernel compile, I can drive up utilization up to almost 30 watts, which means less than 3 hours of battery life. So that’s definitely the good news; Linux can sharply reduce its power consumption to the point where it is highly competitive with Windows. (And probably better than Vista, just because that OS is so heavy and bloated.) So thanks and and a tip of the hat to Intel and to Arjan van de Ven for making such a useful tool like Powertop available.

So now for the bad news. Getting down to this level of power saving thriftness, where the laptop is carefully sipping only the minimal amounts of power from the battery, is definitely a work in progress. First of all, you can only get this level of power savings by unloading a specific USB driver, uhci_hcd. This will disable low speed devices (including unfortunately the fingerprint reader and the EVDO WWAN device if you were silly enough to buy one that was built into the laptop as opposed to a stand-alone card that you can swap between laptops and lend out to friends as necessary). But how many users are going to open up a terminal window, su to root and type the command “rmmod uhci_hcd”? And know how to reload the driver using “modprobe uhci_hcd” when they need to use the USB devices again?

A similar problem exists for Network Manager; when the user disables the network by right-clicking on the applet, why doesn’t it automatically bring down the interface, instead of forcing the user to manually su to root and then type the command “ifconfig eth0 down; ifconfig wlan0 down”?

A more serious problem is the Intel Wireless driver for the 4965. Even with the wlan0 interface configured down, and with the RF kill switch enabled, keeping the iwl4965 driver loaded will still cost you an extra full watt of power. When you’re down to 9.6 watts, that means that keeping the iwl4965 driver loaded when you don’t need it will cost you a 10% reduction in your battery life! That’s just sloppy, and hopefully it will be fixed in a future update to the iwl4965 driver, but as long as you don’t mind manually removing and reloading it, you can work around this power-saving oversight.

A bigger issue, though, one for which no workaround exists, is that unlike the ipw3945 drivers, which at least had private, non-standard iwpriv commands to engage the 802.11’s power-saving features, the iwl4965 driver has neither the non-standard Intel iwpriv interfaces, nor the standard iwconfig interfaces for enabling any kind of powersaving features, including changing the transmit power of the card. So while powertop deserves plenty of   kudos, iwl4965 deserves a wag of the finger from a power saving viewpoint. No doubt Intel just needs to allocate more money to its Open Source Technology Center so it get more of its crack developers to work improving Linux support for their processors and chipsets.

Speaking of which, I’m still waiting for an Intel x.org 965GM driver that can support compiz/beryl and simultaneously show video clips at the same time… And being able turn off the 50 interrupts/second generated by the video card when they aren’t needed because 3-d graphics aren’t currently in use, without requiring a restart of the X server, would also be a nice touch. The bottom line is that Linux power savings and Linux support for laptops in general is much better than it was a year ago, and a lot of credit has to go to the efforts of Intel’s teams producing such good work as powertop, their wireless drivers, and their open X server drivers. We still have a lot of work left to be done, though!

Sous Vide, Revisited

Published October 8th, 2007 in Cooking | 12 Comments »

In a previous post, I had recommended the 4130 NIST-Traceable Temperature Controller to control the temperature in a slow cooker. Unfortunately, that particular controller has a range that tops out at 60 degrees C / 140 degrees F, which is enough for cooking beef for long periods of time, but not enough for say, cooking duck confit, which for which a sous vide temperature of 80 degrees C is recommended. In addition, the 4130 is pretty expensive; almost $150. It’s possible to add a resistor to change the range of the 4130, but the temperature displayed by the controller is no longer correct, and you have manually create a conversion table between true temperature and the temperature as seen by the controller.

I’ve recently come across a cheaper and better possibility, the Ranco ETC-111000-000 Temperature Controller which is only half the price and comes with a much larger working range (-30 to 220 degrees F). The price with the AC cord already wired in is $75; and the version which just has a 120VAC SPDT relay is only $60.

A bit more about food safety. There has always been a lot of concern about bacteria growth and botulism, for good reason — and so therefore the recommendations for cooking temperature have a lot of safety margin in them — to the point now that the USDA recommends that steaks be cooked to at least 145 degrees F, which is well within what had traditionally been called “medium”, and chicken to at least 165 degrees F, which is enough to really destroy taste and texture. Sous vide cooking, especially some of the more low temperature variants, have raised a lot of concerns, to the point where a few years ago New York City (temporarily) banned it, causing a great outcry in the foodie community, since many top restaurants use sous vide techniques.

First of all, any recommendation about internal temperatures and food safety that doesn’t also factor in time is massively oversimplifying the problem. Here is a table taken from “Food Safety Hazards and Controls for the Home Food Preparer”, published by the Hospitality Institute of Technology in 1994:

Temperature, F Time, 5D kill Time, 6.5D kill
130 86.42 minutes 112.34 minutes
135 27.33 minutes 35.53 minutes
140 8.64 minutes 11.23 minutes
145 2.73 minutes 3.55 minutes
150 51.85 seconds 1.12 minutes
155 16.40 seconds 21.32 seconds
160 5.19 seconds 6.74 seconds
165 1.64 seconds 2.13 seconds

This table lists the time to reduce bacteria concentrations of Salmonella and E. coli from 100,000 to 1 (5D) or 3,162,277 to 1 (6.5D). The FDA and USDA recommend cooking hamburger to 5D destruction. Since it is extremely unlikely for there to be more than 100 Salmonella organisms per gram of meat, a 5D kill will reduce Salmonella concentrations to no more than 1 organism per kilogram. So whether you cook a piece of meat to an internal temperature of 165 degrees for 1.64 seconds, or hold it at 130 degrees for 90 minutes, the effect on Salmonella and E. coli bacteria will be the same.Of course, one concern is that in many forms of cooking, particularly oven roasting and grilling, the temperature of the food as it heats up may not be even; so how do you guarantee that all parts of the food product has been brought up to the requisite 165 degrees? One way that recipe authors, fearful of liability concerns, have done so is to tell people to cook meat to much higher internal temperatures, to provide that extra safety margin at the expense of dessicated, horribly tasting turkey or chicken. But the advantage of sous vide cooking is by immersing the food in a water bath, the excellent heat conductivity of water helps guarantee that the entire body of meat will get raised to desired temperature relatively quickly. (How quickly depends on the thickness of the meat, obviously). So if you hold a roast beef that has been vacuum packed in a Foodsaver bag for five or six hours, there should be no question that all of the common bacteria has been inactivated, and that amount of time at 130 degrees F should be sufficient to inactivate 99.9 percent of all botulism toxin molecules (not there should be any in a fresh piece of meat, of course!)

However, sous vide temperatures are not enough to kill bacterial spores, in particular C. botulinum, which is responsible for botulism. This requires temperatures far in excess of boiling water at sea level. For example, home canning protocols recommend holding the food product at 250 degrees F for at least 15 minutes. This is an issue in the restaurant business because very often food would be cooked sous vide, and then stored in the vacuum sealed bags for potentially weeks (yes, you could be eating an extremely expensive meal at a top-end French restaurant that had been cooked several weeks ago, and reheated just before serving; yummy, no?). If the food packages aren’t cooled quickly enough, and then allowed to warm to the danger zone, it’s possible that in the anerobic environment the C. botulinum spores could germinate and then start producing toxin. But, if you are cooking home sous vide where you are serving the food right after it has been cooked, this shouldn’t be a concern.

Hans Reiser, 20/20, and his talk at Google

Published October 4th, 2007 in Filesystems, OSS | 4 Comments »

I got a call from one of the researchers from ABC news this evening. Apparently they are planning on doing a segment on Hans Reiser on their 20/20 show, and the researcher knew enough that there were some serious technical inaccuracies with the script (at the level of “so when Hans was creating reiser4, was that software; was he writing a program?” and “does the program run on the hard drive?”), and so they were looking for help on some technical issues on a background basis. She didn’t take any quotes from me; what she needed was help understanding the technical issues around filesystems and Linux. I tried to help explain what a filesystem was that would make sense to a lay person in 15 seconds; I have no idea whether the researcher got it, and whether she’ll be able to make changes in the script that will be vaguely coherent. We’ll see. I spent a lot of time working with Joshua Davis, providing background material for his Wired article, and he still got a bunch of the technical details wrong. The 20/20 researcher did ask me some silly questions such as “whether we were surprised when murder charges were filed against Hans?” Well, yes. What did she expect me to say? “Oh, yes, were always worried someone would get hurt…” Not! Sigh…. I might not agree with Hans’s filesystem design principles or his tactics in trying to get reiser4 accepted, but I always respected him as a fellow open source programmer.

The researcher mentioned to me that Hans had done a talk at Google that was available at the Google Video site. Out of curiosity, I took a look at it. It was interesting; the last time I had seen Hans was in 1999, at the Linux Storage Management Workshop in Darmstadt, Germany that was organized by Matthew O’Keefe at Sistina Software. Compared to how he looked back then, and the picture of him in the Wired article, taken a 10-12 months after his talk at Google in February, 2006, I was struck by how much heavier (and older at least compared to my memory of him, which was much closer to this picture from his resume) in the Google Video. I also remember him as being a much more dynamic and energetic speaker, and I was struck by how slowly he spoke, with lots of long pauses and “umms” and “ahhs”. He seemed to be a much better public speaker in Darmstadt, but in the Google talk he seemed very tired as he gave the talk.

One of the questions that the researcher asked me was whether I thought he was a genius or not. I told her that I thought he was quite bright in terms of raw intelligence, but that his Social IQ wasn’t as high as you might want for someone to be successful in gathering volunteers to work on an Open Source project, and in working with others in an Open Source development community. Looking at the video, I think that is very much true. He was a terrible public speaker, but some of the points he made about optimizing B-tree algorithms made sense. I might disagree with his philosophy over filesystem design and benchmarking, and I might not be terribly impressed by his social skills, but in terms of being a talented computer scientist, he was and is that.

Is he guilty of the crime that he has been accused of? I have no idea. But from looking at his talk and knowing what I know of him, I have the sense of a greek tragedy. He’s been working on some of his ideas since his undergraduate days in UC Berkely in the early eighties — which he entered after finishing his 8th grade. And as research ideas, I think he might have gotten some very interesting results out of trying some of the things that he wants to do around operating system namespaces. (I think they are doomed in a production system descended from Unix, since application programmers are unlikely to rewrite their programs to take advantage of reiserfs’s performance characteristics — which would mean instead of using a Unix-like configuration file, treating a directory hierarchy containing the configuration information like a Windows registry. Still, as an academic, Plan 9-like system, I could have seen it has being a potentially very interesting Systems Research effort.) Unfortunately, his skills at public speaking and his ability to work with other people have handicapped him, and I know that has frustrated him deeply. So I have a lot of sympathy for him, and I hope that he is innocent, and will be found innocent. But only time will tell….

Anyway, according to the researcher, they are currently scheduling their segment about Hans on 20/20 on October 19th. I’m sure that schedule is subject to change, but it’ll be interesting to see how they treat Hans in their coverage. Hopefully it will be fair, and not overly sensationalistic, but unfortunately my faith in today’s TV edutainment-focused news program isn’t terribly high. My impression was that the research wanted to do a good job, but she was burdened by a very tight deadline, and in the end, the decision of what goes on the air and what doesn’t won’t be up to her. So we’ll see.