[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Onto the second talk
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Steve Capper is going to tell us\Nabout the good bits of Java
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,They do exist
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,[Audience] Could this have been a \Nlightening talk? [Audience laughter]
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Believe it or not we've got some \Ngood stuff here.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I was as skeptical as you guys \Nwhen I first looked.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,First apologies for not attending this\Nmini-conf last year
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I was unfortunately ill on the day \NI was due to give this talk.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Let me figure out how to use a computer.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Sorry about this.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,There we go; it's because \NI've not woken up.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Last year I worked at Linaro in the \NEnterprise group and we performed analysis
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,on 'Big Data' applications sets.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,As many of you know quite a lot of these \Nbig data applications are written in Java.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I'm from ARM and we were very interested\Nin 64bit ARM support.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So this is mainly AArch64 examples \Nfor things like assembler
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,but most of the messages are \Npertinent for any architecture.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,These good bits are shared between \Nmost if not all the architectures.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Whilst trying to optimise a lot of \Nthese big data applications
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I stumbled a across quite a few things in \Nthe JVM and I thought
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,'actually that's really clever; \Nthat's really cool'
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So I thought that would make a good \Nbasis for a talk.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This talk is essentially some of the \Nclever things I found in the
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Java Virtual Machine; these \Noptimisations are in Open JDK.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Source is available it's all there, \Nreadily available and in play now.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I'm going to finish with some of the \Noptimisation work we did with Java.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,People who know me will know \NI'm not a Java zealot.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I don't particularly believe in \Nprogramming in a language over another one
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So to make it clear from the outset \NI'm not attempting to convert
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,anyone to Java programmers.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I'm just going to highlight a few salient \Nthings in the Java Virtual Machine
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,which I found to be quite clever and \Ninteresting
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and I'll try and talk through them \Nwith my understanding of them.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Let's jump straight in and let's \Nstart with an example.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is a minimal example for \Ncomputing a SHA1 sum of a file.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I've alluded some of the checking in the \Nbeginning of the function see when
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,command line parsing and that sort of \Nthing.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I've highlighted the salient points in red.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Essentially we instantiate a SHA1 \Ncrypto message service digest.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And we do the equivalent in \NJava of an mmap.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Get it all in memory.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And then we just put this status straight \Ninto the crypto engine.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And eventually at the end of the \Nprogram we'll spit out the SHA1 hash.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,It's a very simple programme
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,It's basically mmap, SHA1 output \Nthe hash afterwards.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,In order to concentrate on the CPU \Naspect rather than worry about IO
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I decided to cheat a little by \Nsetting this up.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I decided to use a sparse file. As many of\Nyou know a sparse file is a file that not
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,all the contents are necessarily stored \Non disc. The assumption is that the bits
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,that aren't stored are zero. For instance\Non Linux you can create a 20TB sparse file
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,on a 10MB file system and use it as \Nnormal.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Just don't write too much to it otherwise \Nyou're going to run out of space.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The idea behind using a sparse file is I'm\Njust focusing on the computational aspects
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,of the SHA1 sum. I'm not worried about \Nthe file system or anything like that.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I don't want to worry about the IO. I \Njust want to focus on the actual compute.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,In order to set up a sparse file I used \Nthe following runes.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The important point is that you seek\Nand the other important point
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,is you set a count otherwise you'll fill your disc up.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I decided to run this against firstly \Nlet's get the native SHA1 sum command
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,that's built into Linux and let's normalise these results and say that's 1.0.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I used an older version of the Open \NJDK and ran the Java programme
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and that's 1.09 times slower than the \Nreference command. That's quite good.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Then I used the new Open JDK, this is now\Nthe current JDK as this is a year on.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And 0.21 taken. It's significantly faster.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I've stressed that I've done nothing \Nsurreptitious in the Java program.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,It is mmap, compute, spit result out.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,But the Open JDK has essentially got \Nsome more context information.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I'll talk about that as we go through.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Before when I started Java I had a very \Nsimplistic view of Java.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Traditionally Java is taught as a virtual \Nmachine that runs byte code.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Now when you compile a Java program it \Ncompiles into byte code.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The older versions of the Java Virtual \NMachine would interpret this byte code
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and then run through. Newer versions would\Nemploy a just-in-time engine and try and
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,compile this byte code into native machine code.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,That is not the only thing that goes on\Nwhen you run a Java program.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,There is some extra optimisations as well.\NSo this alone would not account for
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,the newer version of the SHA1 \Nsum beingsignificantly faster
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,than the distro supply one.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Java knows about context. It has a class \Nlibrary and these class libraries
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,have reasonably well defined purposes.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,We have classes that provide \Ncrypto services.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,We have some misc unsafe that every \Nsingle project seems to pull in their
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,project when they're not supposed to.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,These have well defined meanings.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,These do not necessarily have to be \Nwritten in Java.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,They come as Java classes, \Nthey come supplied.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,But most JVMs now have a notion \Nof a virtual machine intrinsic
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And the virtual machine intrinsic says ok \Nplease do a SHA1 in the best possible way
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,that your implementation allows. This is \Nsomething done automatically by the JVM.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,You don't ask for it. If the JVM knows\Nwhat it's running on and it's reasonably
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,recent this will just happen \Nfor you for free.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And there's quite a few classes \Nthat do this.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,There's quite a few clever things with \Natomics, there's crypto,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,there's mathematical routines as well. \NMost of these routines in the
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,class library have a well defined notion \Nof a virtual machine intrinsic
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and they do run reasonably optimally.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,They are a subject of continuous \Noptimisation as well.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,We've got some runes that are \Npresented on the slides here.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,These are quite useful if you \Nare interested in
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,how these intrinsics are made.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,You can ask the JVM to print out a lot of\Nthe just-in-time compiled code.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,You can ask the JVM to print out the \Nnative methods as well as these intrinsics
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and in this particular case after sifting \Nthrough about 5MB of text
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I've come across this particular SHA1 sum\Nimplementation.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is AArch64. This is employing the \Ncryptographic extensions
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,in the architecture. So it's essentially \Nusing the CPU instructions which
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,would explain why it's faster. But again \Nit's done all this automatically.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This did not require any specific runes \Nor anything to activate.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,We'll see a bit later on how you can \Nmore easily find the hot spots
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,rather than sifting through a lot \Nof assembler.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I've mentioned that the cryptographic \Nengine is employed and again
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,this routine was generated at run \Ntime as well.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is one of the important things about \Ncertain execution of amps like Java.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,You don't have to know everything at \Ncompile time.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,You know a lot more information at \Nrun time and you can use that
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,in theory to optimise.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,You can switch off these clever routines.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,For instance I've got a deactivate \Nhere and we get back to the
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,slower performance we expected.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Again, this particular set of routines is \Npresent in Open JDK,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I think for all the architectures that support it.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,We get this optimisation for free on X86 \Nand others as well.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,It works quite well.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,That was one surprise I came across \Nas the instrinsics.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,One thing I thought it would be quite \Ngood to do would be to go through
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,a slightly more complicated example. \NAnd use this example to explain
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,a lot of other things that happen \Nin the JVM as well.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I will spend a bit of time going through \Nthis example
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and explain roughly the notion of what \Nit's supposed to be doing.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is an imaginary method that I've \Ncontrived to demonstrate lot of points
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,in the fewest possible lines of code.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I'll start with what it's meant to do.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is meant to be a routine that gets a\Nreference to something and let's you know
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,whether or not it's an image and in a \Nhypothetical cache.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,I'll start with the important thing \Nhere the weak reference.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,In Java and other garbage collected \Nlanguages we have the notion of references.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Most of the time when you are running a \NJava program you have something like a
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,variable name and that is in the current \Nexecution context that is referred to as a
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,strong reference to the object. In other \Nwords I can see it. I am using it.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Please don't get rid of it. \NBad things will happen if you do.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So the garbage collector knows \Nnot to get rid of it.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,In Java and other languages you also \Nhave the notion of a weak reference.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is essentially the programmer saying\Nto the virtual machine
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,"Look I kinda care about this but \Njust a little bit."
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,"If you want to get rid of it feel free \Nto but please let me know."
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,This is why this is for a cache class. \NFor instance the JVM in this particular
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,case could decide that it's running quite \Nlow on memory this particular xMB image
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,has not been used for a while it can \Ngarbage collect it.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The important thing is how we go about \Nexpressing this in the language.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,We can't just have a reference to the \Nobject because that's a strong reference
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and the JVM will know it can't get \Nrid of this because the program
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,can see it actively.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So we have a level of direction which is known as