.NET (Core and Framework)

1-Dec-06 5:42

Hi,

Does anyone ever manipulate the L1, L2 cache directly when writing managed application for Windows? Is it possible to load the whole application in L1 or L2 cache. I was told by my boss I should load my application into L1 or L2 cache for performance reason. As I've never written such code before, I'm wondering whether it can be done. Hope you guys can give me a few pointers.

Thanks,
chew

Dan Neely1-Dec-06 7:15

Dan Neely

1-Dec-06 7:15

AFAIK you can't do it directly, since the processor keeps whatever it used most recently in the cache. What you can do is make the inner loop of your most computationally intensive section of code small enough that it can fit in the cache entirely. You also want to write it so the working set of your data will also fit in the data cache completely.

--
Rules of thumb should not be taken for the whole hand.

kkchh1-Dec-06 14:01

1-Dec-06 14:01

Thanks. Does that also mean I can't manipulate the cache if I'm writing unmanaged application using language such as unmanaged c++.net?

chew

Dave Kreskowiak1-Dec-06 16:38

1-Dec-06 16:38

What kind of performance benefit do you think you'll get over the Windows Task Scheduler and the on-chip Cache Manager?

More importantly, without regard to its feasibility, what would it cost you to develop such a mechanism versus it's best POSSIBLE performance benefit? (Assuming there are no side-effects on the rest of the system, of course)

Now, recalculate that cost, throwing in developing fixes for the inevitable problems something like this will generate.

Is it really worth it?

Dave Kreskowiak
Microsoft MVP - Visual Basic

kkchh1-Dec-06 17:38

1-Dec-06 17:38

Hi,

Pardon me. I've yet to develop an application that needs to take into consideration on windows task scheduler and on-chip cache manager. I don't have any comment on that. I was told it will be faster to move data from L1, L2 cache. I'm not sure how significant in term of performance. Do you think you can enlighten me from your experience?

Thanks,
chew

Dave Kreskowiak2-Dec-06 7:17

2-Dec-06 7:17

The last time I saw that little trick being used was under DOS way back in the day. I don't see any possible way of doing it under Windows. At least that has any decent performance benefit. Remember, your application is only a few threads running in a sea of a few hundred of them. Back under DOS, your app had total control of the entire system. Under Windows, that's never the case. If you try and monopolize even a quarter of either cache with your own code and data, what impact is that going to have on the rest of the system and applications that are running?

Minimizing cache swaps for your code/data means that other code/data are going to get swapped more often. So great! You get a performance benefit for your app, but you can only get that benefit by taking the performance away from something else. In my book, that warrants uninstalling your app.

I'm not your enemy here! Big Grin | :-D

Your boss is! Seriously, does he know what the cost of even attempting to develop such a solution would be?

Is minimizing cache swaps going to be the best performance benefit and use of that money? No, it's not. The thing that slows your app down FAR more is the time your app isn't even executing any code because the single processor machine is executing hundreds of other threads. If you can increase the priority of your application, your threads can get back to the top of the scheduler sooner and spend less time idling. Now that's easy to do with the Thread[^] class. But like I said, you can't get a benefit for free.

Dave Kreskowiak
Microsoft MVP - Visual Basic

kkchh3-Dec-06 6:25

3-Dec-06 6:25

Thanks again. I'll keep your advice in mind.

chew

Profilers

Tristan Rhodes1-Dec-06 1:52

Tristan Rhodes

1-Dec-06 1:52

I'm looking for a good, free .net profiler to generate reports on function execution times.

Apparently .net has one built in, but i can't find anything about it.

Can someone point me in the right direction, or recomend an alternative?

Cheers

Tris

Pete O'Hanlon1-Dec-06 2:56

Pete O'Hanlon

1-Dec-06 2:56

You could always try this one:

http://nprof.sourceforge.net/Site/Description.html[^]

I believe that the profiler you are looking for in .NET is in VSTS (I only have Professional so I can't help you there).

Arthur Dent - "That would explain it. All my life I've had this strange feeling that there's something big and sinister going on in the world."
Slartibartfast - "No. That's perfectly normal paranoia. Everybody in the universe gets that."

Deja View - the feeling that you've seen this post before.

Dave Kreskowiak1-Dec-06 4:36

1-Dec-06 4:36

Tristan Rhodes wrote:
Apparently .net has one built in, but i can't find anything about it.

That depends on which version of Visual Studio .NET you're using. 2002 and 2003 don't have them, but 2005 does, and it depends on which Edition of VS.NET 2005 you have.

Dave Kreskowiak
Microsoft MVP - Visual Basic

Thomas Stockwell2-Dec-06 16:13

Thomas Stockwell

2-Dec-06 16:13

Which versions of VS.NET 2005 have a built in profiler. I use VS.NET 2005 Academic Standard Edition.

Regards,
Thomas Stockwell

Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.

Visit my homepage Oracle Studios[^]

Dave Kreskowiak2-Dec-06 17:10

2-Dec-06 17:10

Professional and above. None of the Academic versions have any profilers.

Dave Kreskowiak
Microsoft MVP - Visual Basic

Thomas Stockwell3-Dec-06 3:16

Thomas Stockwell

3-Dec-06 3:16

Thanks

Interfacecasting

Hendrik Debedts30-Nov-06 22:43

Hendrik Debedts

30-Nov-06 22:43

What's the meaning of casting from a class to an interface?

Guffa30-Nov-06 23:13

Guffa

30-Nov-06 23:13

It means that you tell the compiler that instead of the reference to a specific class that you have, you want a reference to the same object but the type of the reference should be one of the interfaces that the class implements.

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b { font-weight: normal; }

Hendrik Debedts1-Dec-06 0:15

Hendrik Debedts

1-Dec-06 0:15

I know, but what is the need of doing this? Why should someone do this?

Guffa1-Dec-06 1:16

Guffa

1-Dec-06 1:16

Hendrik Debedts wrote:
I know

So that's why you asked? Wink | ;)

Hendrik Debedts wrote:
but what is the need of doing this? Why should someone do this?

To get a reference to an interface. If you for example use the Array.Sort method with an IComparer, you need a reference to an IComparer:

Array.Sort(SomeArrayOfMine, MyOwnComparer);

Here, the reference to the MyOwnComparer object is implicitly casted to IComparer.

---
b { font-weight: normal; }

Hendrik Debedts1-Dec-06 8:26

Hendrik Debedts

1-Dec-06 8:26

Yes ok, but if you can cast an object to an interface, it means that the class of the object implements the interface and when the class implements the interface you don't have firstly cast the object to the interface

PIEBALDconsult1-Dec-06 9:01

PIEBALDconsult

1-Dec-06 9:01

You wouldn't cast a class to an interface, it's unnecessary. But you may need to go the other way.

If you have two classes (A and B) that implement an interface (I), you may have a method that takes a parameter of type I

public void F ( I i )

then inside the method you may need to cast the parameter to it's actually type (however, this may be poor style)

<br />
{<br />
    if ( i is A ) { (A) i = blah blah blah }<br />
    else<br />
        if ( i is B ) { (B) i = blah blah blah }<br />
        else throw something perhaps<br />
}<br />

but when calling F you needn't cast your instance to I

<br />
A a = new A() ; <br />
F ( (I) a ) ; // legal, but needless<br />
F ( a ) ; // prefered<br />

Scott Dorman1-Dec-06 10:34

Scott Dorman

1-Dec-06 10:34

PIEBALDconsult wrote:
You wouldn't cast a class to an interface, it's unnecessary

This is sometimes necessary. If you have a class that implements two interfaces, each with a method of the same name you will need to explictly cast to the appropriate interface in order to access the correct method.

public interface IList {
   public void Add(object x);
}
 
public interface IDictionary {
   public void Add(object x);
}
 
public class Test : IDictionary, IList {
}
 
Test t = new Test();
((IList)t).Add(x);
((IDictionary)t).Add(x);

Without the explicit cast the compiler will not know which Add method you intended to call.

-----------------------------
In just two days, tomorrow will be yesterday.

PIEBALDconsult1-Dec-06 12:22

PIEBALDconsult

1-Dec-06 12:22

Ew.
I sit corrected. I should have put in more qualifications like "usually unnecessary".
But then you're probably getting into the reason C# only supports single inheritance.