Robert Love

Spain in Diorama

2010-07-27T08:00:00.004-04:00

So I got married.

For our honeymoon, we rented a sporty convertible and took off on a road trip around Spain. Three weeks, 3485 kilometers, fifteen Michelin stars.

I built these "dioramas" of places we visited.

Granada in Diorama

San Sebastián in Diorama

Barcelona in Diorama

Igeldo in Diorama

Hopefully the marriage will stick.

Linux Kernel Development, Third Edition

2010-07-22T07:30:00.005-04:00

I'll mention this only once, promise.

The third edition of my best-selling Linux kernel primer, Linux Kernel Development, is now shipping. The publisher is Addison-Wesley and you can find the book in better local and online booksellers.

What's new? Lots. The text is clarified, reworked, and reorganized. The material is fully updated and now based on the 2.6.34 kernel. I also note if and how the 2.6.32 kernel differs, as that release is a "long-term stable" version and thus likely relevant to many readers.

New material includes treatment of the Completely Fair Scheduler, an analysis of the flusher threads component to page writeback, and a chapter devoted to kernel data structures.

Whether you already own an earlier edition, whether you are a kernel developer or just curious how it all works, Linux Kernel Development is an excellent addition to your bookshelf. But don't take my word for it. From one of the many five-star Amazon reviews (this one of the second edition):

The content is one part why this book is great, but I think bigger points go to Robert Love's delivery. His style is casual yet not willy nilly. A subject like the kernel is both dense and minutia-filled and in turn is so much easier to grasp when it's not presented in a dry academic style. The way I would characterize this book—it's as if you're older brother took you aside and taught you how to hack the mainframe.

And:

I have been doing Linux kernel/system level development on and off since 1999. This is the book that I think should be owned by any Linux newbie who wants [to get into] kernel hacking. Even if people do not directly do Linux kernel development, it is a good book complementary to any serious operating systems course in college—it helps gain a better idea of how and why.

Buy it from Amazon.

Buy it from Barnes & Noble.

Buy it from the publisher.

Micro Four Thirds

2010-04-28T08:00:00.007-04:00

Wanting a lighter kit than the Canon 5D Mark II for my honeymoon, I recently jumped on the Micro Four Thirds bandwagon with a purchase of the Olympus E-PL1 and Panasonic 20mm pancake lens.

This crazy sunset is my first shot:

Sunset over Boston's Back Bay

Shot in JPEG, not RAW, and oversharpened a bit, but the image quality is quite good. What's with the grey sky and bright red sunlight?

iPhone OS 4 and Multitasking

2010-04-08T13:30:00.026-04:00

What follows is a first-look at the just-announced multitasking features in the next iPhone OS. It is solely my opinion.

As I predicted in my previous post on the iPad & iPhone and multitasking, Apple is adding multitasking-like support to iPhone OS 4. And as I wildly speculated, that support is largely (although not completely) in the form of background services. Let's take an initial look.

First, as I wrote in my previous post, both the iPad and iPhone support multitasking today. At the system level, many processes run concurrently, and Apple-provided applications are allowed to multitask. What we are discussing here when we say "multitasking" is specifically the ability for third-party applications to multitask.

Second, this is a very early look at what Apple announced at today's event, which is still going on as I type this. Thus, cut me some slack. Developers should consult more detailed documents, which ought to crop up over the next few days and weeks.

What did Apple announce? A lot of spin, actually, but also two simple features. These features do not allow third-party applications to multitask. That is, on iPhone OS 4, as with now, only one applications runs at a time. What these new features do enable is functionality that fulfills many of the same use cases as multitasking. Let's look at them:

Services. Apple is adding a set of service APIs that allow background processes access to a subset of the device's functionality. Such services have access to, at least, notifications, geolocation, deferred computation, VoIP, and media playback. Having a service API limits the ability of background applications to run errant and destroy battery, but that is not a primary concern. As I stated in my previous post, the real concern with multitasking on an embedded, swapless device is memory consumption. Battery life is a straw man. So how do services solve the memory consumption problem? Alone, as described in the event, they don't. But iPhone OS will continue to kill applications that leave the foreground. Thus, applications will need to be refactored to provide a background component that only uses the new Service APIs. Without the risk of unbounded multitasking, memory pressure is greatly relieved.

Serialization. This was tacked onto the end of the discussion of the new services API, as if it was another service. But it is not. Described as "fast app switching" during the event, this is essentially a serialization API. When apps exit, they may choose to save their state to the backing store. When they restart, they reload this state. iPhone OS provides a simple object serializer today, called NSCoder. It is unclear if Apple is just pushing for better use of this class, or if they are adding additional APIs to make serialization both easier and more powerful. Either way, this will make it appear as if applications are actually multitasking—even though they are not—by allowing them to recover their exact state on restart.

So what about these solutions is "gonna be the best?" Nothing. In fact, what was announced is not even multitasking. Moreover, the new functionality isn't anything that other platforms don't offer today. Android, for example, provides excellent support for both of these features via Services and Bundles, respectively. The new iPhone APIs are not novel. But, despite the spin, that isn't what matters. All that matters is the user. If these APIs are sufficiently robust, they will benefit the user by enabling developers to make better apps.

One difference between Android and iPad & iPhone is that Android does not kill applications on task switch. The iPad & iPhone will continue to do so. Thus, in some sense, Android has a third solution to application multitasking: We allow apps to actually multitask until the system experiences memory pressure, at which point our OOM killer is able to kill applications in least-recently-used order. Then, our serialization solution kicks in, making their reload transparent to the user.

Why the iPad and iPhone don’t Support Multitasking

2010-04-03T17:34:00.024-04:00

Why don't the iPad and iPhone support multitasking? The answer isn't what you think.

There is a lot of misconception around support for multitasking in the iPhone and its giant cousin, the iPad. What follows is my analysis of the situation. I am not privy to any insider Apple information. Moreover, while my knowledge is certainly colored by my work on Android, I’m not drawing a comparison or using any Google-specific knowledge.

First, obviously the iPhone and the iPad do support multitasking. This is 2010 and both are built on modern, powerful operating systems that provide support for preemptive multitasking. Indeed, at the system level, there are many processes running concurrently. And some Apple-provided applications, such as the music player, clearly multitask.

So let’s redefine the complaint. What in actuality is not supported is the ability for third-party applications to multitask. That is, the system enforces a policy whereby once an application leaves the foreground, it terminates. In some ways, this makes sense. The iPad and iPhone user interfaces are single window, single document. Not allowing for background applications probably works out for a whole lot of use cases.

Apple says they do not support multitasking because it is a hamper to stability and a drain on battery life. That clearly isn’t true—the iPad has plenty of processing power and battery capacity. Rumor is that Apple is going to add multitasking in a future OS release. This rumor likely is true. Is Apple somehow going to make background applications not consume any battery? Of course not. These excuses are straw men.

The real reason that the iPad and iPhone do not allow third-party applications to multitask is likely more complex, more technical. Bear with me here. Both the iPad and iPhone, as mobile devices, have limited memory (256MB in the current incarnations) and no hard drive. No hard drive means no swap file. Limited memory and no swap imply that applications have a small, fixed amount of memory at their disposal. They don’t have the luxury of seemingly-infinite memory, as a modern system with swap has. Memory consumption is thus a critical system constraint. Like most systems, the iPad and iPhone deal with this by killing applications that use too much memory via a mechanism called the out of memory (OOM) killer. Unlike most systems, applications designed for the iPad and iPhone know how much memory they have at their disposal, and are designed to operate within those constraints. This is classic memory management in embedded programming. No swap, fixed memory, you deal.

What would happen if third-party applications could multitask? Some number of applications would be in the background. But each application was written presuming it had access to some fixed amount of memory. Thus, if the background applications consumed too much memory, the operating system would have to kill them. But the user would expect that he or she could switch back to an old application, and it would still be running where it was left. He or she certainly doesn’t expect applications to just die every time a new application is run, losing state and even data.

Simply put, the reason the iPad and iPhone do not support multitasking is because it is hard to allow multitasking in a system with no swap and a limited amount of memory. Apple could enable multitasking—indeed, there is no reason that the devices couldn’t support it right now, with a one or two line code change—but your applications would constantly be killed. That isn’t a very useful feature.

So how is Apple going to enable support for multitasking? Likely similar to how Android allows it. The Android platform was designed from the ground up for use on phones and other embedded devices. Consequently, we built in a mechanism whereby applications can save their state, including their current view, with the system. In fact, through this state saving mechanism, which we call Bundles, Android applications can operate as if they are stateless.

Thus, allowing for multitasking on Android is easy. Like the iPad and iPhone, we have a powerful, modern operating system (in Android’s case, based on the Linux kernel). Unlike the iPad and iPhone, we also have Bundles, which allow apps to save their state. Android’s OOM killer is aware of background applications and is capable of killing them in least-recently-used order. If the user switches back to an application that has been killed, the Android platform reloads the application’s state via Bundles. The whole process is seamless. Because Android has this state-saving framework, multitasking is feasible even on a device with limited memory and no swap.

In summary, the iPad and iPhone don’t support multitasking not because it would hurt battery life, but because it is hard to do so on a swapless, embedded device without platform support for serialization, which the devices lack. It is likely that Apple will add the requisite functionality in a future OS release. Until then, enjoy your giant iPhone. Or rock a Nexus One, which multitasks.

Update: Folks have asked me how a serialization system such as Bundles enable support for persistent applications, such as music players or IM clients. You wouldn't want these applications killed, even in low memory situations, and their state is ever changing so saving it isn't productive. There are many ways Apple can provide this support. On Android, we do so via Services. Most applications use the Bundle framework to save their state and are thus easily interruptible. Applications that provide a service to other applications, are a server, or function as a long-running background task use the Service framework. These applications are managed by the system more like Unix daemons and are not killed in least-recently-used order when memory is low.

Web Search Infrastructure

2010-02-10T09:00:00.006-05:00

Lately, I have been working on something different…

Suggest with navigation result, geolocation, and weather result

Caterpillar, Lost

2010-01-21T09:35:00.005-05:00

Defrosting in the Caribbean. Sun & sand. Carib & books.

Lost Caterpillar, Rendezvous Bay, Anguilla, BWI

Content with the world, as if consulted in its creation.

Google Maps Navigation

2009-10-28T11:30:00.001-04:00

The future is here:

Google Maps Navigation

Google announces Google Maps Navigation for Android: 3D turn-by-turn GPS navigation with real-time maps and traffic. For free. Shipping first on the Verizon Droid.

Other features:

Voice search
Street View integration: See a photo of your next turn or the destination
Search along route: Find a gas station on your current road
Satellite view

For more information: Google Maps Navigation for Android.

Linux in a Nutshell 6ed

2009-10-13T15:30:00.010-04:00

I've been spending more cycles tweeting than blogging, so I know I don't get to mention this here but once. Yet I am excited to announce the sixth edition of Linux in a Nutshell, the book that DesktopLinux calls the "most complete and authoritative command reference for Linux."

I suspect many of this blog's readers consider themselves beyond the need for a Linux reference, but Linux in a Nutshell is an essential book for new and advanced Linux users alike, with the sixth edition going well beyond your basic file utilities and system management. For example, highlights of this edition include,

A primer on Linux virtualization, including KVM, libvirt, VMware, and Xen
In-depth discussion on the ip command, which replaces ifconfig and the other components of net-tools
A primer on source control management, including entire chapters dedicated to Subversion and Git
An introduction to Upstart, a replacement for the init daemon
Topics you only pretend to master: awk, sed, and vim
A majestic horse on the cover
And, of course, a complete command reference, networking primer, and system management guide

Even graybeards will find something new in the introduction to virtualization or the guide to ifconfig's replacement. And, let's be honest, Git is more complicated than the US tax code, but with this new edition you will be branching and rebasing in no time.

Linux Journal's 2009 Readers' Choice awards voted Linux in a Nutshell the best Linux book of all time. Buy your copies of Linux in a Nutshell today!

Tiananmen, Then and Now

2009-06-05T14:00:00.004-04:00

Yesterday marked the 20th anniversary of the Tiananmen Square massacre. Today, The Big Picture, the Globe's photo blog, put up a touching remembrance. The changes—the disconnect, the growth—between these two pictures, 1989 and today, are striking:

Changan Avenue, near Tiananmen Square, 1989

Changan Avenue, near Tiananmen Square, 2009

When I was last in China, my blog was blocked by the great firewall. That's me, a rabble rouser. I rouse rabble.

Cupcake!

2009-05-08T16:00:00.004-04:00

For users: Top 10 features you'll love about Android 1.5

For developers: Download SDK 1.5

Where I've Been

2009-03-31T04:00:00.006-04:00

I have been silent, I know. Both work and life keep me busy. At work, we released Android 1.1, which added voice search, Latitude, and paid apps. We continue to advance the platform, with exciting upcoming releases including the anticipated cupcake milestone. And of course there will be more phones.

In life, I spend most of my blogging cycles on my food blog (feed), knocking out several posts a week—that is not just a lot of blogging, but quite a bit of braising, infusing, roasting, and even foam making.

I find myself again with pen to paper—nothing anytime soon—and am happy to announce two new translations of Linux Kernel Development: Korean and Simplified Chinese. These new, updated, translations reflect the latest printing of the second edition. Find them at your local bookseller.

Also, I got engaged.

Outside Bankie Banx's Dune Preserve, Rendevzous Bay, Anguilla, Inauguration Day

But the largest reason for the radio silence is that a lot of my blogging is on economics and I do not have any insight into our current situation. It is disingenuous to blog otherwise. I don't have a great hold on what is going on, and neither do most commentators, including many economists. If the top macroeconomists are without agreement, I am not sure what a trade economist can add, let alone I.

That said, I did say this, seven months before AIG's liquidity crisis:

The problem: As CDS contracts are not collateralized or otherwise guaranteed, their real value depends on the creditworthiness of the involved parties. The CDS contracts are being marked to market as sizable profit, but if a series of defaults hit, can the reinsuring parties pay the hedgers?

Six months ago, I wrote that while the societal and economic situation is not as bad as during The Great Depression, the financial situation is worse. I believe that continues to be true. But therein lies our problem: This is largely a financial, not an economic, mess, thus our tonic is financial, not economic. Few outside of Wall Street fully understand the esotericism that led us here. Yet few inside of Wall Street are trusted by the public. The Obama administration, led by Secretary Geithner, continues to balance that opposition with a "fix" rather than "replace" Wall Street approach. That is my policy prescription, too.

Let's hope it works.

Happy New Year

2008-12-31T14:00:00.005-05:00

This New Year's Eve, while you drink and dine and dance, as sapping as this roller coaster of a year has been, never take for granted what you have and who you are.

I'm luckier than most.

The Big Picture, The Globe's beautiful photography blog, features an amazingly well composed photo tour of Israel and Hamas's deterioration after six months of relative but illusive calm.

Even they are luckier than some.

Whither an Automotive Industry

2008-12-03T10:30:00.004-05:00

I have long argued, partly in jest, mostly serious, that America should just get out of the car industry altogether and focus our capital on things we are good at, such as the service sector, software, or torts. The cost issue was secondary, I would say, if the cars themselves aren't competitive. (Does everyone at GM have huge fingers? Why are the interiors filled with over-sized plastic buttons?)

My bafflement continues with this latest bailout—unlike the financial package, I am against bailing out the US auto industry—and these comments from Ford's chief on the necessity of action:

Ford said in its plan that it could survive through 2009 with its current cash levels and by tapping its credit line with private banks, and that it could return to profitability by 2011. Even though it is better prepared for the downturn, Ford said it wanted $9 billion in loans to draw upon if necessary.

Ford’s chief executive, Alan R. Mulally, said the prospect of a failure of G.M. would cascade through the entire domestic auto industry and put millions of jobs at risk.

"We are very, very concerned, and that’s why we went with G.M. and Chrysler to Congress even though we think we have sufficient liquidity," he said in an interview.

Mulally is saying Ford is financially secure and does not need the bailout to meet payments, but he is worried about the second stage effects from a GM or Chrysler failure.

That seems backwards to me. Ford—and every other car manufacturer—would assuredly benefit from two of its competitors going under. There would be a small drop in demand as supply falls and prices rises, but that drop would be significantly smaller than the decrease in supply. Moreover, the substitution from GM to other manufacturers would overly favor Ford, in contrast to Mulally's statements, as "buy American" types swap one Detroit icon for another. The converse has the government funding a broken GM, propping up supply to the detriment of Ford. I don't get it.

I suppose Mulally could be bluffing, hoping to look good in the eyes of Wall Street and Ford's creditors but still get government help—to have his cake and eat it too. But somehow I doubt his posturing is worth the risk.

I love this city tonight, I love this city always

2008-11-04T09:00:00.005-05:00

I will be live-twittering tonight's election results.

Boston, mid autumn

As I wrote four years ago: If you are informed and have an opinion, please vote. Laziness is not an excuse. Although voting for Ralph Nader is.

The Economist Endorses Senator Obama

2008-10-30T16:00:00.003-04:00

The Economist endorses Senator Obama for President.

The why is summed up in part by the endorsement—"if only the real John McCain had been running"—and in part by last week's Conservatives for Obama, so-called Obamacon:

The biggest brigade in the Obamacon army consists of libertarians, furious with Mr Bush’s big-government conservatism, worried about his commitment to an open-ended "war on terror," and disgusted by his cavalier way with civil rights.

Of course, the endorsement should be no surprise. The Economist has a history of endorsing the other party: Governor Reagan in 1980, Governor Clinton in 1992, Senator Dole in 1996, Governor Bush in 2000, and Senator Kerry in 2004.

With this heady endorsement, the Illinois senator might just win.

Android is Now Open Source

2008-10-21T11:30:00.004-04:00

Via my coworkers at the Android Developers Blog: Android is now open source.

Android is the first free, open source, and fully customizable mobile platform. Android offers a full stack: an operating system, middleware, and key mobile applications. It also contains a rich set of APIs that allows third-party developers to develop great applications.

Across my career, I am most proud of Android—as a platform, as a family of phones, and as a catalyst for change in an otherwise closed industry. But the most exciting part is what's next. Download the SDK and start hacking.

Android!

2008-10-02T12:00:00.004-04:00

Download the Android SDK 1.0 release 1.

Walt Mossberg: "The first real competitor to the iPhone ... the software is slick ... the G1 is a powerful, versatile device."

But the sui generis: Android is open to developers, open to consumers, and open to handset manufacturers. Cannot wait to see what's next.

Just Do Whatever Bernanke Says

2008-09-29T12:00:00.006-04:00

The Journal has a great primer on this morning's compromise bailout bill.

Do read the article, but the gist is this: The Treasury will initially have $250b, and up to $700b, to buy either directly or via auction bad loans and assets from financial institutions, in return for warrants for equity. Compromise language includes disincentives for high CEO pay, additional congressional oversight, and a surprising requirement for the president "to submit a legislative proposal to seek reimbursement from the financial institutions that participated" if the value of the purchased assets yields a net loss.

The best analogy I can come up with to describe the crisis is the lemon problem, exasperated by mark to market accounting: Balance sheets are full of mortgage-backed or otherwise related assets, the popping of the housing bubble resulted in a revaluation of these assets, and capitalization requirements are driving banks to liquidate the assets. Enter the lemon market. Is the bank selling the assets because it needs cashflow, or because the assets are full of subprime contagion? Is this the firm's best or worst assets? The information asymmetry has snowballed to the point of credit market implosion. Thus the government's first solution, improving lending opportunities. When that was found insufficient, as the last few weeks have witnessed, we enter this second round, where the government actually buys the troubled assets.

It is hard to comprehend how dire this situation is as the economy still "feels" okay. Gas prices might be high, but unemployment is not at 30%. Yet while the societal ramifications are not as bad, the financial conditions are worse than those that kicked off The Great Depression.

Sur la Table

2008-09-16T09:00:00.011-04:00

If you are not reading my food blog, Food Tastes Good, you are missing out on recipes such as …

Spaghetti alla Carbonara con Lobster Mushroom

Slow-Braised Carnitas

Pesto alla Genovese

Wild Mushroom Risotto with Green Peas

Red Wine Braised Beef Short Ribs

If not the actual dishes, at least the pictures are ambrosial.

Some sort of Cat

2008-08-22T14:00:00.001-04:00

The greatest Wondermark ever, if not the greatest thing, ever:

Slightly switching gears, David Leonhardt on Obamonics in the Times.

And, in case you missed it, we released version 0.9 of the Android SDK. Its dreamy.

Broken Elevators

2008-08-09T10:30:00.000-04:00

Via Google's Open Source Blog, this Google-sponsored project to study Linux I/O scheduler behavior is quite interesting, yielding unexpected results—for example, deadline is actually best for some workloads and CFS, while ideal for others, has awful worst-case performance.

Curious about I/O schedulers? Check out chapter 13 in my favorite kernel book. Want to optimize your code's file I/O and understand scheduling from the perspective of user-space? Read chapter 4 in my favorite system programming book.

Hummers, Cristal, and Cambodian Children: Hello, Nouveau Riche!

2008-08-08T10:00:00.000-04:00

Hat tip to loyal reader for making me a billionaire:

Expires six months after issue

Somewhat unrelated, Amazon is running a special this month wherein you can try Amazon Prime Free for One Month—in other words, get a month of gratis two-day shipping. US only, unfortunately.

There is always money in the banana stand

2008-07-19T15:20:00.000-04:00

Zimbabwe introduces $100 billion banknotes, each valued at one US dollar.

In all seriousness, for posterity, I would love to get one or two of these new bills. If anyone can help, I will pay handsomely.

EDGE puts me on Edge

2008-07-11T11:30:00.000-04:00

The line of 3G-hopefuls outside of Boston's Apple Store:

The fervor Apple instills in their customers, particularly compared to their competitor, is impressive.

Incidentally, down the street, the line outside of the decidedly-less cool AT&T Store was only ten or so folks deep.