[MonoTouch] Understanding the impact of trampolines

[slodge]

Thanks Rolf

All seems to make some sense - and at least I understand now that this is
type not instance based. I've not found any easy way to work out the
numbers, so for now I'm increasing all 3 - but only to 2048, not to 4096.
If and when the users start seeing out of memory errors, then I'll know
that this is one of the places where I can try to optimise.

Thanks again

Stuart

On 22 March 2012 23:43, Rolf Bjarne Kvinge [via MonoTouch] <
ml-node+s2284126n4497367h91 at n4.nabble.com> wrote:

> Hi Stuart,
>
> On device we generate all the necessary code at build time in a process
> known as Ahead of Time compilation (similar to Microsoft's ngen), because
> we're not allowed to jit code on devices. Unfortunately there are a few
> things that cannot be determined statically - for instance generic
> interfaces might need different vtables depending on which type the
> interface is instantiated with. (For this case it is technically possible
> to determine the maximum number of vtables, but the number would be
> potentially enormous - multiply the number of generic interfaces times the
> number of types in your app...). We cannot allocate memory for these
> vtables dynamically at runtime, so we've picked a reasonable default and
> allow the user to increase this value if they run into issues. This is the
> basic theory for the trampolines (the exact problem is a bit different,
> depending on the type of trampolines, but that's not really important).
>
> So you can add as many trampolines as you want, but memory usage will
> increase. That's also all there is to it: the app will not get slower
> (unless if the increased memory usage causes it to run slower, due to
> out-of-memory warnings, etc). It also means that you only have to increase
> the number of trampolines of the type you're actually having problems with,
> if you increase the others you'll increase the size of your executable
> needlessly.
>
> I hope this helps,
> Rolf
>
> On Thu, Mar 22, 2012 at 11:17 AM, slodge <[hidden email]<http://user/SendEmail.jtp?type=node&node=4497367&i=0>
> > wrote:
>
>> I've hit a few problems in apps with running out of trampolines -
>> especially
>> because I used DI with lots of interfaces.
>>
>> To get around this I've tried command line changes like:
>>
>> -aot "nrgctx-trampolines=4096" -aot "nimt-trampolines=4096" -aot
>> "ntrampolines=4096"
>>
>> However, I'm not really sure what I'm doing here.... I know the defaults
>> are
>> 1024. What impact does changing these values have on performance, on image
>> size or anything else? Is there any guidance available on these numbers?
>> Does it matter that I'm increasing all 3 values together? Or should I just
>> focus on the one(s) that seem to be giving me problems?
>>
>> Thanks
>>
>> Stuart
>>
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