Re: Can you write code directly in CIL ???

Peter,

You are missing the point completely. If you implement your code as
managed code, even in IL, you can't stop a GC no matter what. Your thread
is going to be pre-empted (in most situations, except if you have the GC
running on a separate thread) and it WILL stop and it WILL affect your
performance when it happens.

Just because your code knows how much memory it needs doesn't mean that
you can pre-empt a GC. If it happens, it's going to happen, and there is
nothing you can do about it. Your 100-line function isn't going to be able
to stop it, and the CLR isn't going to care what your function is doing.

You can't just pretend its not going to happen. It does, and it will,
and you can't stop it. This isn't a choice you have if you are running
managed code, whether you do it in IL or not.

This is what it means to have ^managed^ code. The CLR is going to
provide a good number of services, but you are going to have to pay for
them, and should be aware of how they impact your code.

This is why I recommended that you use interop with your unmanaged code.
You will have your performance requirements fufilled, and not have to worry
about doing something that will ultimately be self-defeating.

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx

"Peter Olcott" <olcott@xxxxxxx> wrote in message
news:GV3sf.37927$QW2.2410@xxxxxxxxxxxxx
>
> "Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote
> in message news:uvvaatpCGHA.4004@xxxxxxxxxxxxxxxxxxxxxxx
>> Peter,
>>
>> You don't understand a fundamental concept to .NET and CIL. Yes,
>> there are compilers that will perform optimization of IL to a certain
>> degree.
>>
>> However, when the managed code is run, the CLR will take the CIL and
>> then compile it into native code. At this point in time, it is free to
>> optimize, or not optimize, or mangle your code in any way you want when
>> making the transition from CIL to native code.
>>
>> When you are dealing with assembly language in general, you have
>> complete control of what is going on, memory allocation, deallocation,
>> execution, etc, etc. With the CLR, this is taken out of your hands to a
>> degree.
>
> I don't care about these things they are not effecting my performance.
> What is effecting my performance are things such as the compiler failing
> to inline my functions code, and unnecessary overhead in the translation
> of a switch statement. My function will be always executed several million
> times every second. It must run concurrently with other applications.
>
>>
>> For example, have you considered, what happens when a Garbage
>> Collection (GC) occurs while your function is running? If it is in
>> complete managed code, then there is nothing that you can do about it,
>> and your function will resume running when the GC is complete. Depending
>> on what is happening on the machine at the time, combined with what your
>> program is doing, etc, etc, it is very feasible that your code will take
>> more than 1/10th of a second.
> My code knows exactly how much memory it needs at load time. It needs all
> of this memory the whole time that it executes. It would make no sense to
> have any garbage collection of my code's memory in this case. I want my
> code to be implemented as a .ET component.
>
>>
>> Just because it looks like assembly language, don't assume that CIL is
>> assembly language. There are some very different things going on under
>> the hood.
>>
>> --
>> - Nicholas Paldino [.NET/C# MVP]
>> - mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> "Peter Olcott" <olcott@xxxxxxx> wrote in message
>> news:xj2sf.37906$QW2.34052@xxxxxxxxxxxxx
>>>I want to be able to stick with purely managed code, if possible. I just
>>>need this 100 line function to run as fast as if it was hand tweaked
>>>assembly language. I have examined CIL, for the most part it is
>>>essentially assembly language. From what I understand any optimizations
>>>take place before the CIL is generated. When I designed this system (in
>>>1998) I had hand tweaked assembly language in mind for this crucial
>>>function all along.
>>>
>>> "Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote
>>> in message news:%23RjK3$oCGHA.2040@xxxxxxxxxxxxxxxxxxxxxxx
>>>> Peter,
>>>>
>>>> Not at all. When the CLR gets a hold of the JIT, it is free to
>>>> perform any optimizations it deems necessary, and that might not
>>>> necessarily be in line with what you are expecting.
>>>>
>>>> My recommendation would be to use Managed C++ to create a wrapper to
>>>> your unmanaged code which uses It Just Works (IJW, seriously). You
>>>> should get a managed interface, and the best possible performance (for
>>>> this specific situation, not all situations) between managed an
>>>> unmanaged code.
>>>>
>>>>
>>>> --
>>>> - Nicholas Paldino [.NET/C# MVP]
>>>> - mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>>
>>>> "Peter Olcott" <olcott@xxxxxxx> wrote in message
>>>> news:_51sf.37898$QW2.37853@xxxxxxxxxxxxx
>>>>>I need the best possible execution speed. I have found that there is a
>>>>>large difference in the quality of the code generated by the various
>>>>>compilers. I have 16,000 hours of development time in my current
>>>>>project. There is a 100 line function that must take no longer than
>>>>>1/10 second to execute. I can just barely achieve this with MSVC++ 6.0.
>>>>>MSVC++ 7.0 has had some of its optimizations disabled. I eventually
>>>>>will need to port this to C# .NET. This is a case where hand tweaked
>>>>>assembly language would be appropriate. I figured that hand tweaked CIL
>>>>>would be the .NET equivalent of hand tweaked assembly language.
>>>>>
>>>>> "Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
>>>>> wrote in message news:OCvd7unCGHA.2644@xxxxxxxxxxxxxxxxxxxxxxx
>>>>>> Peter,
>>>>>>
>>>>>> You can write it, but you would have to create a module with IL,
>>>>>> and then compile that into your assembly (or just write the whole
>>>>>> assembly).
>>>>>>
>>>>>> Also, what optimizations do you think you can make? Ultimately,
>>>>>> you suffer from the fact that Windows is not a real-time OS, and
>>>>>> nothing you can do will change that. On top of that, the JIT is
>>>>>> what's going to optimize your code again after you try to, so you
>>>>>> might actually end up hurting yourself more than helping yourself.
>>>>>>
>>>>>> If you post the code you are trying to optimize, we can try and
>>>>>> tell you where you might make some improvements, but dipping down to
>>>>>> the IL level is most likely not going to help you much.
>>>>>>
>>>>>>
>>>>>> --
>>>>>> - Nicholas Paldino [.NET/C# MVP]
>>>>>> - mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>>>>
>>>>>>
>>>>>> "Peter Olcott" <olcott@xxxxxxx> wrote in message
>>>>>> news:7t%rf.37887$QW2.9998@xxxxxxxxxxxxx
>>>>>>> Cab you write code directly in the Common Intermediate language? I
>>>>>>> need to optimize a critical real-time function.
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>


.

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