[llvm-dev] MCJit Runtine Performance

[Lang Hames via llvm-dev]

Hi Morten,

Something else just occurred to me: can you share your EngineBuilder configuration lines? (http://llvm.org/docs/doxygen/html/classllvm_1_1EngineBuilder.html)

In particular - are you explicitly setting the optimization level? The old JIT may have had a different default.

- Lang.



Sent from my iPad

> On Feb 4, 2016, at 10:54 PM, Jim Grosbach via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> I agree with Lang and Keno here. This is both unexpected and very interesting. Given the differences in defaults between the two, I would have expected the new JIT to have better performance but longer compile times. That you are seeing the opposite implies there is something very wrong and I'm very interested to help figure out what it is. 
> 
> Sent from my iPad
> 
>> On Feb 4, 2016, at 9:12 PM, Morten Brodersen via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> 
>> Hi Keno,
>> 
>> I am talking about runtime. The performance of the generated machine code. Not the time it takes to lower the IR to machine code.
>> 
>> We typically only JIT once (taking a few secs) and then run the generated machine code for hours. So the JIT time (IR -> machine code) doesn't impact us.
>> 
>> Cheers
>> Morten
>> 
>>> On 05/02/16 15:58, Keno Fischer wrote:
>>> Actually, reading over all of this again, I realize I may have made the wrong statement. The runtime regressions we see in julia are actually regressions in how long LLVM itself takes to do the compilation (but since it happens at run time in the JIT case, I think of it as a regression in our running time). We have only noticed occasional regressions in the performance of the generated code (which we are in the process of fixing). Which kind of regression are you talking about, time taken by LLVM or time taken by the LLVM-generated code?
>>> 
>>>> On Thu, Feb 4, 2016 at 11:44 PM, Rafael Espíndola <llvm-dev at lists.llvm.org> wrote:
>>>> On 4 February 2016 at 22:48, Morten Brodersen via llvm-dev
>>>> <llvm-dev at lists.llvm.org> wrote:
>>>> > Hi Rafael,
>>>> >
>>>> > Not easily (llc).
>>>> >
>>>> > Is there a way to make MCJit not use the large code model when JIT'ing?
>>>> >
>>>> 
>>>> I think Davide started adding support for the small code model.
>>>> 
>>>> Cheers,
>>>> Rafael
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>> 
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