[petsc-users] %T (percent time in this phase)

[Barry Smith]

> On Sep 28, 2021, at 12:11 PM, Karthikeyan Chockalingam - STFC UKRI <karthikeyan.chockalingam at stfc.ac.uk> wrote:
> 
> Thanks for Barry for your response.
>  
> I was just benchmarking the problem with various preconditioner on cpu and gpu. I understand, it is not possible to get mutually exclusive timing.
> However, can you tell if KSPSolve time includes both PCSetup and PCApply? And if KSPSolve and KSPSetup are mutually exclusive? Likewise for PCSetUp and PCApply.

   If you do not call KSPSetUp() separately from KSPSolve() then its time is included with KSPSolve().

   PCSetUp() time may be in KSPSetUp() or it maybe in PCApply() it depends on how much of the preconditioner construction can take place early, so depends exactly on the preconditioner used.

   So yes the answer is not totally satisfying. The one thing I would recommend is to not call KSPSetUp() directly and then KSPSolve() will always include the total time of the solve plus all setup time. PCApply will contain all the time to apply the preconditioner but may also include some setup time.

  Barry

>  
> Best,
> Karthik.
>  
>  
>  
>  
> From: Barry Smith <bsmith at petsc.dev>
> Date: Tuesday, 28 September 2021 at 16:56
> To: "Chockalingam, Karthikeyan (STFC,DL,HC)" <karthikeyan.chockalingam at stfc.ac.uk>
> Cc: "petsc-users at mcs.anl.gov" <petsc-users at mcs.anl.gov>
> Subject: Re: [petsc-users] %T (percent time in this phase)
>  
>  
> 
> 
> On Sep 28, 2021, at 10:55 AM, Karthikeyan Chockalingam - STFC UKRI <karthikeyan.chockalingam at stfc.ac.uk <mailto:karthikeyan.chockalingam at stfc.ac.uk>> wrote:
>  
> Hello,
>  
> I ran ex45 in the KPS tutorial, which is a 3D finite-difference Poisson problem. I noticed from the output from using the flag -log_summary that for various events their respective %T (percent time in this phase) do not add up to 100 but rather exceeds 100. So, I gather there is some overlap among these events. I am primarily looking at the events KSPSetUp, KSPSolve, PCSetUp and PCSolve. Is it possible to get a mutually exclusive %T or Time for these individual events? I have attached  the log_summary output file from my run for your reference.
>  
>  
>   For nested solvers it is tricky to get the times to be mutually exclusive because some parts of the building of the preconditioner is for some preconditioners delayed until the solve has started. 
>  
>   It looks like you are using the default preconditioner options which for this example are taking more or less no time since so many iterations are needed. It is best to use -pc_type mg to use geometric multigrid on this problem.
>  
>   Barry
>  
>  
> 
> 
> Thanks!
> Karthik.
>  
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> <ksp_ex45_N511_cpu_6.txt>

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