更多RAM的使用一般，我們說的RAM是手機的工作記憶體，而進行運算時使用的是快閃記憶體。當然，這只是一個簡單的說法，而在”設定”的項目下你可以找到關於Android目前的記憶體使用狀況。前面提過Android 4.0是在1GB RAM的硬體下而生的，那對於普遍的512MB硬體來說呢？將有340MB被用作Linux user space(Linux使用者空間)，而將僅剩下三分之一做為一般的使用。而許多ICS的運用程式，比起薑餅都會占用更多記憶體空間，像是瀏覽器就比薑餅上的多了20~30MB之譜。
一個良好的做法，HTTP請求與資料庫操作並不應該在主要的使用中進行，但Sony的工程師發現ICS有不少這種狀況，不斷的在主要的工作中操作資料庫，這可能會導致其他的工作變慢。此外，根據目前許多不滿意的使用者的說法，我們可以支看到許多對於應用程式與遊戲上的問題。如果應用程式的讀取浪費太久的時間，將可能會出現Application Not Responding (應用程式沒有回應，ANR)。ANR的狀況會發生在應用程式沒有回應任何資訊，或是沒在限定的時間內回應。
Ever thought about how Gingerbread (GB) and Ice Cream Sandwich (ICS) platforms differ on a technical level? In this blog post, we’ll describe some of the technical differences between GB and ICS, and what the differences in the user experience might be. This way you can decide if ICS is right for you, or if you prefer to stay on Gingerbread. Maybe you will prefer the new UI in ICS, or do you give a higher priority to the extreme stability of the Gingerbread platform? Read more after the jump!
However, although ICS is new and compelling in many ways, we would like all of our users to make an informed decision when selecting what Android™ software to use. We are actually proud to say that our Gingerbread software is very stable and has great performance, so it’s not a bad idea to stay on this release. Ice Cream Sandwich is more intensive, for example in terms of resource usage. As smartphones become more capable, our own applications, as well as the Google Mobile Services (GMS) applications, are becoming more advanced, which means that they require more CPU power, run more network activities and use more RAM. On the other hand, ICS brings a refined UI and some nice new features as described below.
Comparison of the look and feel in Gingerbread (left) and Ice Cream Sandwich (right).
New features in ICSFrom a UI perspective, ICS is based on a new look and feel, the Holo theme. In order to accommodate the new look of Android, we decided to do an extensive touch up of our own assets, since the graphical assets of the Holo theme cannot be changed in any way as stated in the Android Compatibility Definition Document (CDD). New looks have been added in the platform layer as well as in the application layer. All in all, well over a thousand icons have been modified. In addition, we have deployed new wallpapers and application backgrounds, which harmonise more with the flatter graphical structures of ICS.
In ICS, the activity manager has a completely new UI, where all running apps are shown as thumbnails in a list. To close an activity, you can simply swipe it out of the list. ICS also introduces a face recognition app as a way to unlock the phone, called Face Unlock. Face Unlock uses the front-facing camera and advanced object recognition algorithms. It is included in our ICS upgrade for all phones that have a front-facing camera.
The contact list will show more information about the contacts, including updates from social networks. In the calendar, colour coding has been added and it is now possible to zoom. There is also support for a new type of voicemail that is more visual, offering transcriptions of voice messages.
When it comes to ICS, it’s a major upgrade of Android™, and there are a lot of things that have changed compared to the Gingerbread release. Some of these changes affect the performance and stability of the system, for example by using more CPU power and RAM. ICS was developed with Galaxy Nexus in mind, which is based on a TI platform with dual-core processor and 1GB RAM. We are now adapting ICS to run on our 2011 Xperia™ smartphones, which are all built on a Qualcomm platform with single core and 512 MB RAM. This means that in some cases, the resource usage in ICS is heavier on the system compared to Gingerbread. The following sections identify some key areas where there is a difference between ICS and Gingerbread.
Increased RAM usageIn general, it can be said that the RAM is the working memory in the phone, used by running processes in contrast to the flash memory, which is mainly used to store things. As you might understand, this is a simplified explanation and might not be entirely true in all cases. However, it can serve as a help to understand the difference between the RAM and the flash memory of the phone. To see how much RAM is currently used, go to Applications in the Settings app of your Xperia™ phone.
Now, let’s look at how the RAM is used. Out of our 512MB RAM, about a third is used for functions that require a dedicated memory slot to operate fast enough. For example, this is the case for certain multimedia functions. The remaining space, which is at least 340MB, is reserved for the Linux user space, as required in the Android Compatibility Definition Document (CDD). Within the Linux user space, functions like the activity manager and Home screen app are running.
Another interesting thing is that many apps use slightly more RAM in ICS. For example, the web browser is quite intensive, and our measurements indicate that it uses 20-30MB more in ICS compared to Gingerbread. All in all, there are a lot of changes that together result in greater RAM requirement.
Illustration of the RAM usage.
When running low on RAM, typically with less than approximately 40MB left, the activity manager will start to close processes according to priority. At first, idle background activities are killed. The last thing to be closed down is the foreground activity. We have described this briefly in the table below. For more information, check out Android developers. (Please note that all figures mentioned about RAM usage are approximations and will differ depending on phone model and use case.)
Table showing different types of processes. When running out of RAM, the activity manager starts shutting down processes from the bottom and up, so that the last things to close are foreground and persistent activities.
Processes that are closed will obviously have to be restarted when the user enters the app again, which takes time and slows the system down. For example, when running a heavy game that uses all available RAM, the activity manager will be forced to kill all processes running in the background. This might include vital functions like the dialler and even the Home screen application. When you exit your game, there is a risk that the phone is perceived as slow, since the Home screen app will have to be restarted, just like every other activity you access afterwards.
Slower interaction with the SQL databaseAnother change in ICS compared to Gingerbread is that Google has moved a lot of the SQL handling from the native to the Java layer. In our internal studies, we have seen that read and write operations to the SQL database takes longer time, which slows down the apps. Many applications perform a lot of SQL operations when started, which greatly impacts the start-up time.
According to good practice, database operations or http requests should not be performed in the main thread. However, we know that there are quite a few applications that perform these kinds of operations directly in the main thread, which might cause them to hold up other operations. Also, when reading feedback on ICS software out on the market now, we’ve seen comments about people having problems with some applications and games.
If an operation takes too long, there is a risk of getting an Application Not Responding (ANR) as a result. An ANR occurs when an application doesn’t answer an intent, or responds to an input event, within a certain time limit. In case of intent, the time out is set to five seconds. For the input event, such as screen touch or button click, it’s ten seconds.
This can result in a user experience that is perceived as slower and less stable, due to longer response times and increased ANRs.
Introducing full hardware accelerationYet another change in ICS, is that the graphics hardware acceleration is on by default for all apps from API level 14. For apps at lower API levels, it can be turned on in the manifest with the attribute android:hardwareAccelerated=”true”. Hardware acceleration means that the GPU is used to render graphics, which enables a smooth user interface. However, it also results in at need to load additional graphic libraries for certain apps, which makes them use even more RAM.
When we performed internal tests on our applications, we saw that the Settings app consumed 1-2MB more RAM, and actually took longer time to start with HW acceleration, compared to without. Once the app is running, the UI is HW accelerated, but unless the app performs advanced graphics, the user will not see the difference.
Another effect of the hardware acceleration is that it can make the battery drain faster in some cases. An example of this is video playback, where the hardware acceleration requires every video frame to be run through the GPU, thus making the system use more power than it would have without HW acceleration.
As a developer, you should therefore evaluate if HW acceleration is required or not, as it comes with a cost in terms of RAM usage, start-up time and possibly even battery duration which can have negative effects on the user experience. You can read more about hardware acceleration in Ice Cream Sandwich on the Android Developers blog.
So, what will be your platform of choice? We hope this article clarifies some of the aspects to consider when making the decision. As always, we are eager to hear your opinion, so drop us a comment below and let us know! For more details on timing and practicalities on the ICS upgrade, check out this latest post on the Sony Xperia™ Product Blog.
Updated – comment from the Developer World team:
We we would like to clarify that above mentioned “challenges” have already been addressed by our SW engineering teams. For instance, we have not only optimised the RAM management by making the RAM usage for internal apps as good as possible, but we will also introduce a Performance assistant at start up when running ICS. In this Performance assistant, you can enable and disable certain services that you might not want to run on your phone, in order to optimise the performance of your phone.
We have also worked with quite a few partners in regards to architecture optimisations for SQL handling. In addition, we have also optimised the hardware usage. And as a result of this article, a number of app developers have notified us that they are evaluating if HW optimisation will be needed or not for their apps.
The aim of this article was to share our knowledge regarding the different characteristics for ICS and Gingerbread in an open way, as we strive to have an open communication with the developer community. All in all, we would like to point out that it’s our clear aim to deliver an as good ICS update as ever possible. As you might have seen on the Sony Xperia Product Blog, we’re not far from releasing it now. Thanks for all the feedback!