64-Bit Support

ART was designed in mind with modularity of the various target architectures in which it is supposed to run on. As such, it provides a multitude of compiler-backends targeting today’s most common architectures such as ARM, x86 and MIPS. In addition, 64-bit support for ARM64, x86-64 and while still not implemented, also MIPS64.

While we have gone more in depth of the advantages and implications of switching over to 64-bit architectures in the iPhone 5s review, the main points to take away are the availability of an increased address space, generally increased performance, and vastly increased cryptographic capabilities and performance, all while maintaining full 32-bit compatibility with all existing apps.

An important difference that Google is applying over Apple, at least inside VM runtime applications, is that they are using reference compression to avoid the usual memory bloat that comes with the switch to 64-bit. The VM retains simple 32-bit references.

Google has made available some preview benchmarks showcasing the performance gains both on x86 and ARM platforms. The x86 benchmarks were executed on a Intel BayTrail system, and show a 2x to 4.5x speedup in various RenderScript benchmarks. On the ARM side, the crypto performance gains over 32-bit were showcased on an A57/A53 system. Both of these are relatively non-representative of one should really expect in real-world use-cases so they’re not that useful as a performance prediction.

However Google also made some interesting numbers available on one of their internal build-systems called Panorama. Here we can see a 13 to 19% increase in performance by simply switching over the ABI. It is also good to see how ARM’s Cortex A53 is able to make a bigger impact on performance when in AArch64 mode than the A57 cores.

Google claims that 85% of all current Play Store apps are immediately ready to switch over to 64 bit - which would mean that only 15% of applications have some kind of native code that needs targeted recompiling by the developer to make use of 64-bit architectures. This is a great win for Google and I expect the shift over to 64-bit to be very fast once silicon vendors start shipping 64-bit SoCs in the coming year.


In many points, Google has delivered its “Performance boosting thing” and addressed much of the shortcomings that have plagued Android for years.

ART patches up many of the Achilles’ heels that comes with running non-native applications and having an automatic memory management system. As a developer, I couldn’t have asked for more, and most performance issues that I needed to work around with clever programming no longer pose such a drastic problem anymore.

This also means that Android is finally able to compete with iOS in terms of application fluidity and performance, a big win for the consumer.

Google still promises to evolve ART in the future and its current state is definitely not what it was 6 months ago, and definitely not what it will be once the L release is made available in its final form in devices. The future looks bright and I can’t wait to see what Google will do with its new runtime.

Garbage Collection: Theory and Practice
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  • NetMage - Tuesday, July 8, 2014 - link

    I think they could have produced a much better product if they had used C++ instead - native performance and battery life when it was needed in the early days, and probably faster than ios performance today.
  • iAPX - Wednesday, July 2, 2014 - link

    So why not people upgrade if it works so well on Android side?
  • zodiacsoulmate - Thursday, July 3, 2014 - link

    Very impressive
  • mstestzzz000 - Thursday, July 3, 2014 - link

    Inaccuracy in the article:
    "This new allocator, “rosalloc” or Rows-of-Slots-Allocator, ..."

    If you look at the source code for rosalloc (line 39 of https://android.googlesource.com/platform/art/+/ma... they call it "A runs-of-slots memory allocator"
  • Milind - Thursday, July 3, 2014 - link

    I think you are absolutely right there. I doubt that merely doing AOT compiling is going to produce faster results and that's exactly what I experienced when I switched from Dalvik to ART in 4.4. Of course there are going to be more improvements in L since the code itself has improved. I mean who was launching an app on Android and wishing it would *launch* faster? There may have been apps that took their time launching. But not too many. On the other hand, better garbage collection and other improvements will certainly help in run-time performance. AOT is not doing anything much compared to JIT.

    I always wondered why Google didn't buy Sun. Both companies have similar DNA (certainly better than Oracle and Sun) and Android could have used all the expertise Sun had in building JVMs and Real Time Java in Android and the rest of Google. They could have sold off the hardware division to IBM/Oracle and not have had to deal with the heart ache and drama of the lawsuit.
  • Filiprino - Saturday, July 5, 2014 - link

    You'd be amazed on how can evolve a compiler in development stage.
    Most of the performance advantage from ART comes from AOT compilation. It can take the whole code and optimize it agressively. For example, when compiling GCC with the fastest optimizations you can get the whole program executing in the main function, with loop unrollings and vectorizations while taking into account the difference of having the functions inlined, optimizing references to variables and parameter passing.

    A JIT can only focus on the "hot spots", improving some parts of the program but it can't improve it as a whole because there's not enough performance history storage space to achieve that.

    Then, you've got the new Garbage Collection algorithms which improve interactivity quite a lot.
  • seoagile - Thursday, July 3, 2014 - link

    thanks for information.
  • darwinosx - Thursday, July 3, 2014 - link

    So many incorrect statements about jvms in this article it would take a half hour to list them all. Plus nothing at all was said about Googles major motivator which is it is obvious Dalvik was stolen from Sun and the lawsuits aren't over. Finally this is still a long way from true 64 bit and it's benefits. For example the only reason Apple can encrypt and decrypt fingerprints in real time is because encryption operations are dramatically faster in 64 bit.
    Way beneath Anandtech standards.
  • grahaman27 - Saturday, July 5, 2014 - link

    You are correct about apple's decision to use 64bit was partly because of the fingerprint scanner, but you are wrong that L is not fully 64bit compatible. In fact, it is easier for android to move to 64 bit because of the VM it runs on. The Linux kernel has always supported 64bit, but Google's runtime and libraries have not, and consequntly neither have the apps. Android L replaces the libraries and runtime with 64bit compatible versions and "enables" 64bit support for 85% of apps automatically with no work from the developers. That's pretty impressive.
  • PearlCParks - Thursday, July 3, 2014 - link

    Contrary to other mobile platforms such as iOS, Windows or Tizen, whjich run software compiled natively to their specific hardwware architecture, the majority of Android software is based around a generic code language whicjh is transformed from “byte-code” into native insstructions for the hardware on the device itself. The performance gains over Dalvik are significant num.to/427-837-276-945

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