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#ActualRavyne

Posted 24 October 2013 - 01:06 PM


Well, there are many good, sensible points here. And I've heard all of them before. And they are not true...

...

That's true. But so does loop unrolling. That can't be the basis for dismissing __forceinline, it's just another factor to take into consideration. I've never encountered any I$ problems, and I put __forceinline on a 40-lines-of-code-functions more than once.

...


Not always true, not even with the new, much improved VS12 and Intel Compiler 13. Compilers are not, and probably will never be perfect, especially when they need to support a wide variety of CPUs. Sometime you do know better, so why not help the compiler?

 

 

That was my kind of my point, and why I said it wasn't good *blanket* advice--You can't say just use force-inline or don't. Use it when it works, absolutely, but the default should really be to not. The general audience here aren't professionals with multiple years of optimization experience. Not half of them even know the tools they'd need to investigate performance, and fewer still know proper procedures for doing so. Most would, at best, bang up a tight loop that multiplies a bunch of vectors or matrices together, time the competing implementations, pick the winner and never look back afterwards. A good portion of the audience here, being the youngest and least experienced, are simply content to follow hearsay and urban legend as their optimization strategy. In short, you really have to be careful around here to not make statements that could appear as absolute to less-experienced folks because that will do more harm than good. Its better to prescribe the 90% rule, and then identify when a programmer might want to deviate from it.

 

Anyways, we're always glad to have someone with your experience around here (it certainly far exceeds my own) and I'm sure there'll be many more interesting conversations about optimization to come. If you'd ever care to go into depth about optimization work, consider writing an article for the site wink.png


#1Ravyne

Posted 24 October 2013 - 01:04 PM


Well, there are many good, sensible points here. And I've heard all of them before. And they are not true...
 
Ravyne, on 23 Oct 2013 - 4:54 PM, said:

__foceinline ...can blow out your code locality, instruction-cache, and the very small cache of decoded instructions too[/quote]
That's true. But so does loop unrolling. That can't be the basis for dismissing __forceinline, it's just another factor to take into consideration. I've never encountered any I$ problems, and I put __forceinline on a 40-lines-of-code-functions more than once.
 
 

Ravyne, on 23 Oct 2013 - 4:54 PM, said:

the compiler is in a much better position than you to determine whether to inline a particular call-site or not

Not always true, not even with the new, much improved VS12 and Intel Compiler 13. Compilers are not, and probably will never be perfect, especially when they need to support a wide variety of CPUs. Sometime you do know better, so why not help the compiler?
[/quote]

 

That was my kind of my point, and why I said it wasn't good *blanket* advice--You can't say just use force-inline or don't. Use it when it works, absolutely, but the default should really be to not. The general audience here aren't professionals with multiple years of optimization experience. Not half of them even know the tools they'd need to investigate performance, and fewer still know proper procedures for doing so. Most would, at best, bang up a tight loop that multiplies a bunch of vectors or matrices together, time the competing implementations, pick the winner and never look back afterwards. A good portion of the audience here, being the youngest and least experienced, are simply content to follow hearsay and urban legend as their optimization strategy. In short, you really have to be careful around here to not make statements that could appear as absolute to less-experienced folks because that will do more harm than good. Its better to prescribe the 90% rule, and then identify when a programmer might want to deviate from it.

 

Anyways, we're always glad to have someone with your experience around here (it certainly far exceeds my own) and I'm sure there'll be many more interesting conversations about optimization to come. If you'd ever care to go into depth about optimization work, consider writing an article for the site wink.png


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