19-20 july, 2009 | padtad 2009 @ chicago, illinois

© 2009 IBM Corporation

19-20 July, 2009 | PADTAD 2009 @ Chicago, Illinois

A Proposal of Operation History Management System for Source-to-Source Optimization of HPC Programs

Yasushi Negishi, Hiroki Murata and Takao MoriyamaDeep Computing, Tokyo Research Laboratory, IBM Research




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Outline of this Presentation

1.Proposal of an algorithm for managing operation history of source-to-source optimization.

2.Prototype system with new user interface for managing operation history explicitly.



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Background Improvement of single processor performance is stopping, and architectures of

supercomputers is becoming more complex.

– Architecture-specific optimizations are needed to utilize various kinds of network and processor architectures to achieve reasonable performance.

Application areas for numerical simulations continue to expand.

–We need solve performance issues more effectively and more easily.

Source-to-source optimization tools are becoming important.

–Automatic conversion (a.k.a. refactoring) for optimization

–Support typical architecture-specific and application-specific performance optimization patterns.

–Reduce programmer’s time and human errors by supporting routine but troublesome optimization.



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Strength reduction– Replace costly operation with an equivalent but less expensive operation

• E.g. x = r ** (-1) x = 1 / r– Steps

1. Modify the code to use less expensive operation by manual editing Loop unrolling & SIMDization

– Use SIMD instructions If compiler does not generate optimal SIMD instructions in a loop• E.g. x(i) = a(i) + b(i) * c(i) x(i) = FPMADD(a(i), b(i), c(i))• x(i+1) = a(i+1) + b(i+1) * c(i+1)

– Steps1. Unroll the loop by automatic conversion with specifying the range and unroll factor.2. Modify the unrolled loop body with in-line assemble code for SIMD by manual editing

Loop tiling (a.k.a. loop blocking, strip mine and interchange)– Change loop structure to increase memory access locality and cache hit ratio.

• E.g.

– Steps1. Modify the loop by automatic conversion with specifying the range and blocking factors.

Typical Source-to-Source Optimization Steps

for (i=0; i<N; i++) for (j=0; j<N; j++) c[i] = c[i]+ a[i,j]*b[j];

for (i=0; i<N; i+= Bi) for (j=0; j<N; j+= Bj ） for (ii=i; ii<min(i+Bi,N); ii++) for (jj=j; jj<min(j+Bj,N); jj++) c[ii] =c[ii]+ a[ii,jj]*b[jj];

Optimization steps are combinations of automatic conversion and manual editing



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“Reapplication Conflict”

Because of trial-and-error nature of optimization work, it is sometimes required to undo an operation in the past or to insert or change operation in the past even if a single user manages the code.

We call this conflict caused by a single user as “Reapplication Conflict”. System for supporting Source-to-Source optimization should handle this conflict

correctly.



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Issues of Existing Version Management Systems Handling “Reapplication Conflict” Because of trial-and-error nature of optimization work, it is sometimes

required to undo an operation in the past or to insert or change operation in the past even if a single user manages the code.

–We call this conflict caused by a single user as “Reapplication Conflict”.System should handle this conflict correctly.

Existing version management systems use algorithm of “patch” command or similar one to handle conflicts.

But the patch algorithm has a issue.–As for modification by manual editing, the patch algorithm works fine.

• The algorithm applies difference by an operation on different base code, with adjusting target range to be applied.

–As for modification by automatic conversion, the patch algorithm may generate unexpected results.

Scenario in which existing system does not work expectedly is shown.



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Example Scenario of “Reapplication Conflict” (original) program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() do i = 1, n x(i) = i * sin(i / (pi * 4.0d0)) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + x(i) ** (-1) enddo t2 = rtc() - s s = rtc() do i = 2, n b = b + ((x(i) + a) / (pi * 4.0d0) + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Original

Original code is checked out.



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Example Scenario of “Reapplication Conflict” (Step 1) program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, fourpi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() fourpi = pi * 4.0d0 do i = 1, n x(i) = i * sin(i / fourpi) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + x(i) ** (-1) enddo t2 = rtc() - s s = rtc() do i = 2, n b = b + ((x(i) + a) / fourpi + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Original:

Step 1:

Original Operation A

Step 1: Do loop invariant code motion by manual editing, and check it in



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Step 2: Do strength reduction by manual editing, and check it in.


a = 0 b = 0 pi = 3.14159265d0 s = rtc() fourpi = pi * 4.0d0 do i = 1, n x(i) = i * sin(i / fourpi) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + 1.0d0 / x(i) enddo t2 = rtc() - s s = rtc() do i = 2, n b = b + ((x(i) + a) / fourpi + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Original:

Step 1:

Step 2:

Original A B



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Step 3: Do loop unrolling by automatic conversion, and check it in.


a = 0 b = 0 pi = 3.14159265d0 s = rtc() fourpi = pi * 4.0d0 do i = 1, n x(i) = i * sin(i / fourpi) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + 1.0d0 / x(i) enddo t2 = rtc() - s s = rtc() do i = 2, n, 4 b = b + ((x(i) + a) / fourpi + 1.0d0) b = b + ((x(i+1) + a) / fourpi + 1.0d0) b = b + ((x(i+2) + a) / fourpi + 1.0d0) b = b + ((x(i+3) + a) / fourpi + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Original:

Step 1:

Step 2:

Original A B C

Step 3:



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Original:

Step 1:

Step 2:

Original A B C

Step 3:

Step 4: Compile and execute the code, and analyze effects of optimizations

Find the following results Optimization A: not effective Optimization B: effective Optimization C: effective

N.G. O.K. O.K.



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Example Scenario of “Reapplication Conflict” (Step 5)

Original:

Step 1:

Step 2:

Original A B C

Step 3:

Step 5:

Step 5: Undo the optimization A by “patch” command

program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, fourpi, x(n), sin, s, t1, t2, t3, rtc


Target of optimization A

Not target of optimization A, but influenced



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Example Scenario of “Reapplication Conflict” (Final Results) program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() do i = 1, n x(i) = i * sin(i / (pi * 4.0d0)) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + 1 / x(i) enddo t2 = rtc() - s s = rtc() do i = 2, n, 4 b = b + ((x(i) + a) / (pi * 4.0d0) + 1.0d0) b = b + ((x(i+1) + a) / fourpi + 1.0d0) b = b + ((x(i+2) + a) / fourpi + 1.0d0) b = b + ((x(i+3) + a) / fourpi + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Problem:The wrong line is unrolled !!

Because “patch” does not actually apply the automatic conversion operation again, but does just apply difference of the results by automatic conversion operation.

System for managing automatic conversion operations needed.

(1) Adjust the target range

(2) Apply the automatic operation actually again.



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Proposed Algorithm for saving/applying automatic operations Manual editing handled by the patch algorithm

Automatic conversion handled by our proposed algorithm

Originalcode

Optimizationresults

Manual Editing

Context difference file

Saving an operation

Modifiedcode

Applying an saved operation

Optimized results on modified codePatch

algorithm

OriginalCode

Pseudo change file

SpecifyRange

Optimizationresults

Specify Conversion ID and arguments

Operation log


Operation log

Conversion ID

Arguments

ModifiedCode

Pseudo change file

Optimizationresults


Conversion ID

ArgumentsOperation log

Context difference fileOperation log

Patch algorithm Apply automatic

conversion



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Scenario of Proposed Algorism to Save Automatic Operations program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, fourpi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() fourpi = pi * 4.0d0 do i = 1, n x(i) = i * sin(i / fourpi) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + 1.0d0 / x(i) enddo t2 = rtc() - s s = rtc() do i = 2, n b = b + ((x(i) + a) / fourpi + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Algorithm for saving operation history program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, fourpi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() fourpi = pi * 4.0d0 do i = 1, n x(i) = i * sin(i / fourpi) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + 1.0d0 / x(i) enddo t2 = rtc() - s s = rtc()$BEGIN do i = 2, n b = b + ((x(i) + a) / fourpi + 1.0d0) enddo$END t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

pseudo change file

Step 1: Generate pseudo change file by inserting special lines to specify range for the automatic operation.

Step 2: Create context difference file between the file before editing and the pseudo change file

“loop unrolling”

*** opeB.F Sat Jul 11 11:36:34 2009--- opeC2.F Sun Jul 12 13:36:10 2009****************** 19,27 ****--- 19,29 ---- enddo t2 = rtc() - s s = rtc()+ $BEGIN do i = 2, n b = b + ((x(i) + a) / fourpi + 1.0d0) enddo+ $END t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3

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By saving this context difference file, range-adjust algorithm of “patch” command can be used for identifying the target range of automatic conversion.

Step 3: Save identifier of automatic conversion operation (e.g. “loop unrolling”), its parameter (e.g. “4”), and the context difference file as its operation log.

context difference file

parameter

Identifier of automatic conversion Operation log



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Scenario of Proposed Algorism to Apply Automatic Operation (Step 1) program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() do i = 1, n x(i) = i * sin(i / (pi * 4.0d0)) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + x(i) ** (-1) enddo t2 = rtc() - s s = rtc() do i = 2, n b = b + ((x(i) + a) / (pi * 4.0d0) + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end Algorithm for applying operation history

on modified target codeStep1: Apply the context diff file to the target program by using algorithm used by the “patch” command.

Trial 1: Apply the history at the same position

Not Match

Trial 2: Ignore the starting and ending line numbers

Match



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parameter


Trial 3: Ignore outer most one line before/after the modificationTrial 4: Ignore outer most two lines before/after the modification

pseudo change file





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Scenario of Proposed Algorism to Apply Automatic Operation (Step 2)

Algorithm for applying operation history on modified target codeStep2: Redo automatic conversion with its parameter saved in the operation log.



parameter


pseudo change file




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Redo “loop unrolling” “4” times on “the loop”



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Proposed Algorism to Apply Automatic Operation (Final Results)

program sample implicit none integer i, n parameter(n=10000000) real*8 a, b, pi, x(n), sin, s, t1, t2, t3, rtc

a = 0 b = 0 pi = 3.14159265d0 s = rtc() do i = 1, n x(i) = i * sin(i / (pi * 4.0d0)) enddo t1 = rtc() - s s = rtc() do i = 1, n a = a + 1 / x(i) enddo t2 = rtc() - s s = rtc() do i = 2, n, 4 b = b + ((x(i) + a) / (pi * 4.0d0) + 1.0d0) b = b + ((x(i+1) + a) / (pi * 4.0d0) + 1.0d0) b = b + ((x(i+2) + a) / (pi * 4.0d0) + 1.0d0) b = b + ((x(i+3) + a) / (pi * 4.0d0) + 1.0d0) enddo t3 = rtc() - s write(*,*) 'a=', a, 'b=', b write(*,*) 'time=', t1, t2, t3 end

Problem solved.The correct line is unrolled !!

The proposed system can reapply automatic conversion operations correctly.



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Prototype Implementation of the Proposed System

Implemented as an Eclipse plug-in module– Worked with open source CDT/Photran modules– Use CDT/Photran’s C/Fortran parser

Eclipse

Photran module

(Fortran)

Open

SourceHPC refactoring module

CDT module

(C)

Open

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Proposal of user interface for operation history management system

Source code tree view

Information and console output view

Source code view

Operation history view

Operation history view

1. Operation History is displayed as a sequence, and user can select and modify any point of source code.

3. Operations are categorized into the following three categories according to the status and necessity of the reapplication, and are displayed by using three colors.

Green: AppliedYellow: Not tried to appliedRed: Tried to applied, but fail.

2. The succeeding operations are automatically reapplied as needed to produce a new version according to the user’s instructions.



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Conclusion

1.Explained proposal of an algorithm for managing operation history of source-to-source optimization.

2.Explained Prototype system with new user interface for managing operation history explicitly.



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Questions ?

19-20 july, 2009 | padtad 2009 @ chicago, illinois

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