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From Tim Ellison <t.p.elli...@gmail.com>
Subject Re: Anyone plans to enable interpreter + jit in client mode?
Date Wed, 12 Nov 2008 12:33:38 GMT
Aleksey Shipilev wrote:
> On Wed, Nov 12, 2008 at 10:52 AM, Wenlong Li <wenlong@gmail.com> wrote:
>> In my understanding (also from some related work[1]), the startup
>> means the work before executing user's code in main(). So for startup
>> optimization, we may think how to reduce the VM creation time, etc.
> I'm afraid that definition of startup time as "time to get VM
> initialized and ready to execute user code" is loose and does not
> reflect the real impression of startup performance end user wants to
> have. I presume that user wants to minimize the time it gets for code
> to make some work completed: from the moment (s)he invokes JVM to the
> moment JVM outputs the value. That's why SPECjvm2008:startup is
> actually does *one* iteration of each of the benchmark -- just to
> catch up what's the time for VM to initialize, get the user code,
> *execute it* and produce some meaningful result.

That's an important use case -- having the runtime optimized for running
small workloads, such as start-up run a short workload and tear down
(think of script engines etc.); however, I think it is also valid and
valuable to decompose the lifecycle and analyze the work involved with
just the start-up phase.

We did do some work a while ago to make the sharing of ZIP data more
efficient (since Gregory demonstrated that there was excessive bytecode
data copying taking place).  I think there will be additional
optimizations in the class library code for making the start-up quicker.

Profile the start-up to the point of running main() and make that as
slick as possible.  Deferring JIT compilation etc is fine, but the best
efficiency is to "just run less code".

> And so, before actually diving into startup optimizations, it's better
> to have the clue what's consuming the time on SPECjvm2008:startup: "VM
> init takes X usecs", "classloading takes Y usecs, "JET compilation
> takes Z secs", "compiled code takes XX usecs", etc. I had occasionally
> prepared that data 1.5 years ago, so we need to do some fresh start.
> 
> On the class sharing: I'm not sure if it helps in single VM scenario,
> it's more like reducing the time of classloading when neighbor already
> done all the work. Alexey Fedotov have much more expertise on that,
> anyway :)

These are all good areas to explore, and not at all mutually exclusive.

Regards,
Tim

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