What is kernel in android device

What is a kernel?

What is a kernel? If you spend any time reading Android forums, blogs, how-to posts or online discussion you’ll soon hear people talking about the kernel. A kernel isn’t something unique to Android — iOS and MacOS have one, Windows has one, BlackBerry’s QNX has one, in fact all high level operating systems have one. The one we’re interested in is Linux, as it’s the one Android uses. Let’s try to break down what it is and what it does.

Android devices use the Linux kernel, bet every phone uses their own version of it. Linux kernel maintainers keep everything tidy and available, contributors (like Google) add or alter things to better meet their needs, and the people making the hardware contribute as well, because they need to develop hardware drivers for the parts they’re using for the kernel version they’re using. This is why it takes a while for independent Android developers and hackers to port new versions to older devices and get everything working. Drivers written to work with one version of the kernel for a phone might not work with a different version of software on the same phone. And that’s important, because one of the kernel’s main functions is to control the hardware. It’s a whole lot of source code, with more options while building it than you can imagine, but in the end it’s just the intermediary between the hardware and the software.

When software needs the hardware to do anything, it sends a request to the kernel. And when we say anything, we mean anything. From the brightness of the screen, to the volume level, to initiating a call through the radio, even what’s drawn on the display is ultimately controlled by the kernel. For example — when you tap the search button on your phone, you tell the software to open the search application. What happens is that you touched a certain point on the digitizer, which tells the software that you’ve touched the screen at those coordinates. The software knows that when that particular spot is touched, the search dialog is supposed to open. The kernel is what tells the digitizer to look (or listen, events are «listened» for) for touches, helps figure out where you touched, and tells the system you touched it. In turn, when the system receives a touch event at a specific point from the kernel (through the driver) it knows what to draw on your screen. Both the hardware and the software communicate both ways with the kernel, and that’s how your phone knows when to do something. Input from one side is sent as output to the other, whether it’s you playing Angry Birds, or connecting to your car’s Bluetooth.

It sounds complicated, and it is. But it’s also pretty standard computer logic — there’s an action of some sort generated for every event, and depending on that action things happen to the running software. Without the kernel to accept and send information, developers would have to write code for every single event for every single piece of hardware in your device. With the kernel, all they have to do is communicate with it through the Android system API’s, and hardware developers only have to make the device hardware communicate with the kernel. The good thing is that you don’t need to know exactly how or why the kernel does what it does, just understanding that it’s the go-between from software to hardware gives you a pretty good grasp of what’s happening under the glass.

Sort of gives a whole new outlook towards those fellows who stay up all night to work on kernels for your phone, doesn’t it?

Samsung needs to bring back its iPod competitor

I don’t want to buy an iPod Touch. Since I want a reasonably priced PMP with acceptable audio hardware that can install a few crucial apps, I might have to.

VoLTE: How to use it and why you should care

VoLTE — or Voice over LTE — is the new standard for calling throughout the U.S., Canada, and parts of Europe. Not only does it facilitate much higher call quality between cell phones, but it allows devices to stay connected to LTE while on a call, improving data speeds for everyone.

PlayStation reportedly planning service to compete with Xbox Game Pass

Sony is planning to create a service similar to Xbox Game Pass, according to a new report. The service could launch as early as sometime in the spring of 2022, with multiple tiers.

These are the best rugged Android phones

Living the rough and tumble life? Get yourself a smartphone that can handle everything you throw at it — or throw your phone at.

Источник

What is a kernel and why does it matter?

Spend enough time around Android, or even PCs, and eventually, you will come across the term, “the Linux kernel.” Android uses the Linux kernel too. In fact, it’s an integral part of the way your phone works, but what is it?

The “Linux” part is easy enough to understand — it is a play-on-words between Linus and Unix, as in Linus Torvalds, the original creator of the Unix-like OS we call Linux. But kernel? What is a kernel in computers and other devices? What do we mean by the Linux kernel? Let’s find out!

In a nutshell, a kernel is the core program that manages your phone’s CPU resources, the system memory, and the system devices (including the file systems and networking). It is also responsible for managing all the processes or tasks that are running on your smartphone. That means that when you start an app, it is the kernel that loads the app into memory, creates the processes needed, and starts the app running. When an app needs memory, it is the kernel that allocates it. When the app wants networking, it is the kernel that does all the low-level processing.

The driver for devices like Bluetooth is also in the kernel. When the app wants to perform a task in the background, it is the kernel that handles the background threads. When the app closes, it is the kernel that cleans up all the memory and other resources that were used by the app. As you can see, a kernel is a fundamental part that ensures your Android phone actually does what you expect.

What is a kernel: A closer look

All multi-tasking operating systems have a kernel of one form or another. Windows has a kernel, OS X has a kernel, iOS has a kernel, and of course Android has a kernel. But of those, only Android uses the Linux kernel. Windows has its kernel, often referred to as the NT kernel, while OS X and iOS use a kernel known as Darwin.

There are other kernels out there, including Unix-like kernels from the FreeBSD, OpenBSD, and NetBSD projects; real-time kernels from projects like FreeRTOS; embedded kernels from projects like Zephyr; and even low power kernels like the mbed OS kernel from Arm. What this means is that any computing device from an IoT thing or wearable right up to a supercomputer uses a kernel.

The Linux kernel is a complex piece of software. It contains millions of lines of source code. That includes all the drivers (the majority of the code) plus the support for the different system architectures (ARM, x86, RISC-V, PowerPC, etc). When the kernel is built for a particular device, say a smartphone, not all of that source code is used, however even when you strip away what isn’t needed for a particular build, it is still complex.

Monolithic vs microkernel

As with all complex systems, there are different approaches that can be used when it comes to designing a kernel. The Linux kernel is what is known as a monolithic kernel. This means that the kernel is one program using one memory space. The main alternative is the microkernel approach. With microkernels, the essentials of the kernel are placed in the smallest possible program and they interact with other kernel-level programs which run as separate servers or services.

Back in 1992 when Linux was in its early days, Linus Torvalds and Professor Andrew Tanenbaum (who is famous for his books on operating system design and networking) had an online discussion (some say a flame war) about the different merits of monolithic kernel designs versus microkernels. Tanenbaum preferred microkernels and Linus was writing a monolithic kernel. That is now all history as Linux has remained a monolithic kernel, as is the kernel used in Android. If you are interested in a Unix-like microkernel operating system then you should check out Minix 3.

Since Linux is a monolithic kernel there needs to be a way to enable and disable certain parts of the kernel depending on your needs. This is done at compile time using a system that allows the kernel to be tuned, trimmed, and configured as needed. Some of the configurations do more than just activate or deactivate certain functions — they actually change the behavior of the kernel. This is useful when it comes to building and changing smartphone hardware features.

As Linux is open-source, and because the core of Android is itself is open-source thanks to the Android Open Source Project (AOSP), there is a community of developers and enthusiasts that provide alternative kernels for Android smartphones. However, their popularity and availability are dependent on the exact make and model of your device.

How Android uses Linux

On the surface, Android is a nice launcher, some apps like the Chrome web browser or your social media apps, and maybe some games. But there is more going on than meets the eye. Underneath the user interface, there are lots of subsystems, libraries, and frameworks.

For apps to run (either natively or in a Java Virtual Machine) Android provides lots of libraries and frameworks for things like notifications, location services, fonts, web rendering, SSL, window management, and so on. There is also a special service called the SurfaceFlinger, which is responsible for compositing all the different things that need to be drawn into a single buffer that is then displayed on the screen.

Beneath the Android-specific libraries and frameworks is the Linux kernel. As well as managing the processes, the memory, and power management, the Linux kernel contains code for all the different chip architectures and hardware drivers it supports. These drivers include the cameras, Bluetooth, Wi-Fi, flash memory, USB, and audio drivers.

Android also adds some special features to the Linux kernel to make it more suitable for smartphones. These include the Low Memory Killer, a process that monitors the memory state and reacts to high memory demands by killing the least essential processes and so keeps the system running, and wake locks, a way for apps to tell the kernel that the device needs to stay on.

Android 8.0 introduced Project Treble, a re-architecture of Android that created a well-defined interface between the OS framework and device-specific low-level software. Using Linux kernel modules, the SoC and the board-specific drivers were split away from the main kernel, meaning that smartphone makers could work on specific features of a device without needing to alter the core kernel. Treble was designed to make it easier for manufacturers to update their smartphones without worrying about the low-level code.

How do smartphone companies tweak the kernel?

Due to the vast diversity of Android devices, the kernel running on each make and model will be slightly different. There will be specific drivers for the SoC, as well as for other modules like GPS, audio, etc. Each smartphone maker will work together with the SoC provider (Qualcomm, MediaTek, etc) to configure the kernel in the most optimal way for any particular model. This means that smartphone makers will often work on device-specific features, override common kernel configurations, and add new drivers to the Linux kernel.

A good example of a common tweak is the CPU scheduler. When the kernel needs to decide which task should run next, and on which CPU core, it uses a scheduler. Most Android smartphones are heterogeneous multi-processor (HMP) systems. That means that not all the cores in the processor are equal. Some are high-performance, while others offer greater energy efficiency. Using the Energy-Aware Scheduler (EAS), the kernel can predict the impact of its decisions on the energy consumed by CPUs, as well as the performance level available.

The parameters for the EAS can be tweaked by smartphone makers to favor greater performance while using more energy, or lower performance while saving battery. The smartphone makers also have the option to replace the scheduler with one of their own devising.

Every smartphone maker strives to configure the kernel in the best way to enable all the features needed while offering the best performance with the highest possible efficiency. Together with the SoC maker, there are engineers who work to tune the software to get the most from the hardware.

Having said that, smartphone makers aren’t beyond making mistakes or making bad decisions about the way they configure the Linux kernel. OEMs have been known to use setups that are too aggressive in the pursuit of good battery life. For example, OnePlus was caught throttling the performance of the OnePlus 9 Pro to preserve battery life, while others have been known to cheat and artificially boost the CPU performance when a benchmark is running.

The future of how Android uses the Linux kernel

One of the negative sides to the success of Linux is that it changes quickly. To provide a level of stability, there are Long Term Support (LTS) versions of the kernel that are supported for several years. The Android Common Kernels (ACKs) are taken from the main Linux kernel and include patches specific to Android.

Starting with Android 11, the ACKs are used to create Generic Kernel Images (GKIs). These are 64-bit Arm kernels that can be used on any device, if the SoC and driver support are implemented in vendor modules. The idea is to address the issue of kernel fragmentation by unifying the core kernel and moving SoC-specific parts out of the kernel and into loadable modules. This in turn will reduce the kernel maintenance burden for OEMs, while separating hardware-specific components from the core kernel.

Android 12 saw the first release of some devices with GKI kernels. Google has committed to regularly releasing signed boot images with critical bug fixes. Because of the binary stability offered by the GKIs, these images can be installed with no changes to vendor images.

The result will be an improvement in the way Google can release newer Linux kernels for general use, which in turn will help improve security, and has the potential to increase the number of years that a device receives updates and fixes. Fingers crossed.

Источник