[Openmp-dev] counts in the work sharing

Mon Mar 16 11:11:28 PDT 2020

Couple of weeks ago Jim Cownie <jcownie at gmail.com<mailto:jcownie at gmail.com>> effectively answered your question.

Let me try to re-iterate:
> For each static_init_4 call, there is a static_fini call. Is this specific to its static_init_4 call?
Yes.

> Is there a pairing of calls that can not be broken?
Yes, though I am not completely sure what you are asking about here.  You can break the code any way you want, but why?

> If we look at the static_fini call, the function arguments are the same.
Same as what?  They are probably same location info and global thread id as in the corresponding static_init call, if I got your question right.

> It seems that if we have two static_init_4 function calls, we can interchange their static_fini calls. Does that make sense?
Not sure what is your goal here… All you can achieve by such broken code generation is to confuse an OMPT tool with unspecified results, possibly break statistics gathering, break checking of consistency of the OpenMP constructs, - all the code of static_fini does.

> If I move the static_fini call beyond Loop-B in IR; Should Loop-B be part of the Work Sharing environment and its iteration should be distributed similarly to Loop-A over the available threads?
All you can achive here is again to get broken code generation, and as a result to confuse an OMPT tool with unspecified results, etc.  The static_fini call does not affect parallelization in any way, so your second Loop-B will remain to be serial loop and will be redundantly executed by all threads of the team, regardless of the location of the static_fini call.  To make a loop work sharing, it should be parallelized (e.g. by adding “#pragma omp for” in the source code, given there exist enclosing parallel region).

As Jim suggested earlier, look at the code!

And please first describe the problem you want to solve. As opposed to trying to shuffle statements by guess.

Regards,
Andrey

From: Abid Malik <abidmuslim at gmail.com>
Sent: Monday, March 16, 2020 5:58 PM
To: Churbanov, Andrey <Andrey.Churbanov at intel.com>
Cc: openmp-dev at lists.llvm.org
Subject: Re: [Openmp-dev] counts in the work sharing

Thanks for the information.

For each static_init_4 call, there is a static_fini call. Is this specific to its static_init_4 call? Is there a pairing of calls that can not be broken? If we look at the static_fini call, the function arguments are the same. It seems that if we have two static_init_4 function calls, we can interchange their static_fini calls. Does that make sense?

Suppose we have two loops, Loop-A and Loop-B ( Loop-A and Loop-B are identical in terms of iteration, chunk, increment, etc). One with omp for loop and other without it

#pragma omp for
{
  Loop-A
}

Loop-B

If I move the static_fini call beyond Loop-B in IR; Should Loop-B be part of the Work Sharing environment and its iteration should be distributed similarly to Loop-A over the available threads?

Thanks,

On Mon, Mar 16, 2020 at 8:04 AM Churbanov, Andrey <Andrey.Churbanov at intel.com<mailto:Andrey.Churbanov at intel.com>> wrote:
For static schedule the runtime does not track iterations.  The __kmpc_for_static_init_4 (or similar, depending on the iteration variable type) is the only runtime call for a statically scheduled loop (not counting leading barrier if any). After it compiler just loops over obtained range of iterations without involving runtime any more.

Regards,
Andrey

From: Openmp-dev <openmp-dev-bounces at lists.llvm.org<mailto:openmp-dev-bounces at lists.llvm.org>> On Behalf Of Abid Malik via Openmp-dev
Sent: Friday, March 13, 2020 9:35 PM
To: openmp-dev at lists.llvm.org<mailto:openmp-dev at lists.llvm.org>
Subject: [Openmp-dev] counts in the work sharing

Hello,

I am looking into the void __kmp_for_static_init4 function which marks the start work sharing. The function computes the upper and lower bounds and stride to be used for the set of iterations to be executed by the current thread from the statically scheduled loop that is described by the initial values of the bround, stride, increment and chunk size.  How the record of iterations is kept. Which function/file should I look into to keep track of the iteration?

Thanks,

--
Abid M. Malik
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"I have learned silence from the talkative, toleration from the intolerant, and kindness from the unkind"---Gibran
"Success is not for the chosen few, but for the few who choose" --- John Maxwell
"Being a good person does not depend on your religion or status in life, your race or skin color, political views or culture. IT DEPENDS ON HOW GOOD YOU TREAT OTHERS"--- Abid
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Abid M. Malik
******************************************************
"I have learned silence from the talkative, toleration from the intolerant, and kindness from the unkind"---Gibran
"Success is not for the chosen few, but for the few who choose" --- John Maxwell
"Being a good person does not depend on your religion or status in life, your race or skin color, political views or culture. IT DEPENDS ON HOW GOOD YOU TREAT OTHERS"--- Abid
"The Universe is talking to us, and the language of the Universe is mathematics."----Abid

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