Actual source code: ex47cu.cu

petsc-3.13.4 2020-08-01
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  1: static char help[] = "Solves -Laplacian u - exp(u) = 0,  0 < x < 1 using GPU\n\n";
  2: /*
  3:    Same as ex47.c except it also uses the GPU to evaluate the function
  4: */

  6:  #include <petscdm.h>
  7:  #include <petscdmda.h>
  8:  #include <petscsnes.h>

 10: #include <thrust/device_ptr.h>
 11: #include <thrust/for_each.h>
 12: #include <thrust/tuple.h>
 13: #include <thrust/iterator/constant_iterator.h>
 14: #include <thrust/iterator/counting_iterator.h>
 15: #include <thrust/iterator/zip_iterator.h>

 17: extern PetscErrorCode ComputeFunction(SNES,Vec,Vec,void*), ComputeJacobian(SNES,Vec,Mat,Mat,void*);
 18: PetscBool useCUDA = PETSC_FALSE;

 20: int main(int argc,char **argv)
 21: {
 22:   SNES           snes;
 23:   Vec            x,f;
 24:   Mat            J;
 25:   DM             da;
 27:   char           *tmp,typeName[256];
 28:   PetscBool      flg;

 30:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
 31:   PetscOptionsGetString(NULL,NULL,"-dm_vec_type",typeName,256,&flg);
 32:   if (flg) {
 33:     PetscStrstr(typeName,"cuda",&tmp);
 34:     if (tmp) useCUDA = PETSC_TRUE;
 35:   }

 37:   DMDACreate1d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE,8,1,1,NULL,&da);
 38:   DMSetFromOptions(da);
 39:   DMSetUp(da);
 40:   DMCreateGlobalVector(da,&x); VecDuplicate(x,&f);
 41:   DMCreateMatrix(da,&J);

 43:   SNESCreate(PETSC_COMM_WORLD,&snes);
 44:   SNESSetFunction(snes,f,ComputeFunction,da);
 45:   SNESSetJacobian(snes,J,J,ComputeJacobian,da);
 46:   SNESSetFromOptions(snes);
 47:   SNESSolve(snes,NULL,x);

 49:   MatDestroy(&J);
 50:   VecDestroy(&x);
 51:   VecDestroy(&f);
 52:   SNESDestroy(&snes);
 53:   DMDestroy(&da);

 55:   PetscFinalize();
 56:   return ierr;
 57: }

 59: struct ApplyStencil
 60: {
 61:   template <typename Tuple>
 62:   __host__ __device__
 63:   void operator()(Tuple t)
 64:   {
 65:     /* f = (2*x_i - x_(i+1) - x_(i-1))/h - h*exp(x_i) */
 66:     thrust::get<0>(t) = 1;
 67:     if ((thrust::get<4>(t) > 0) && (thrust::get<4>(t) < thrust::get<5>(t)-1)) {
 68:       thrust::get<0>(t) = (2.0*thrust::get<1>(t) - thrust::get<2>(t) - thrust::get<3>(t)) / (thrust::get<6>(t)) - (thrust::get<6>(t))*exp(thrust::get<1>(t));
 69:     } else if (thrust::get<4>(t) == 0) {
 70:       thrust::get<0>(t) = thrust::get<1>(t) / (thrust::get<6>(t));
 71:     } else if (thrust::get<4>(t) == thrust::get<5>(t)-1) {
 72:       thrust::get<0>(t) = thrust::get<1>(t) / (thrust::get<6>(t));
 73:     }
 74:   }
 75: };

 77: PetscErrorCode ComputeFunction(SNES snes,Vec x,Vec f,void *ctx)
 78: {
 79:   PetscInt          i,Mx,xs,xm,xstartshift,xendshift,fstart,lsize;
 80:   PetscScalar       *xx,*ff,hx;
 81:   DM                da = (DM) ctx;
 82:   Vec               xlocal;
 83:   PetscErrorCode    ierr;
 84:   PetscMPIInt       rank,size;
 85:   MPI_Comm          comm;
 86:   PetscScalar const *xarray;
 87:   PetscScalar       *farray;

 89:   DMDAGetInfo(da,PETSC_IGNORE,&Mx,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE);
 90:   hx   = 1.0/(PetscReal)(Mx-1);
 91:   DMGetLocalVector(da,&xlocal);
 92:   DMGlobalToLocalBegin(da,x,INSERT_VALUES,xlocal);
 93:   DMGlobalToLocalEnd(da,x,INSERT_VALUES,xlocal);

 95:   if (useCUDA) {
 96:     VecCUDAGetArrayRead(xlocal,&xarray);
 97:     VecCUDAGetArrayWrite(f,&farray);
 98:     PetscObjectGetComm((PetscObject)da,&comm);
 99:     MPI_Comm_size(comm,&size);
100:     MPI_Comm_rank(comm,&rank);
101:     if (rank) xstartshift = 1;
102:     else xstartshift = 0;
103:     if (rank != size-1) xendshift = 1;
104:     else xendshift = 0;
105:     VecGetOwnershipRange(f,&fstart,NULL);
106:     VecGetLocalSize(x,&lsize);
107:     try {
108:       thrust::for_each(
109:         thrust::make_zip_iterator(
110:           thrust::make_tuple(
111:             thrust::device_ptr<PetscScalar>(farray),
112:             thrust::device_ptr<const PetscScalar>(xarray + xstartshift),
113:             thrust::device_ptr<const PetscScalar>(xarray + xstartshift + 1),
114:             thrust::device_ptr<const PetscScalar>(xarray + xstartshift - 1),
115:             thrust::counting_iterator<int>(fstart),
116:             thrust::constant_iterator<int>(Mx),
117:             thrust::constant_iterator<PetscScalar>(hx))),
118:         thrust::make_zip_iterator(
119:           thrust::make_tuple(
120:             thrust::device_ptr<PetscScalar>(farray + lsize),
121:             thrust::device_ptr<const PetscScalar>(xarray + lsize - xendshift),
122:             thrust::device_ptr<const PetscScalar>(xarray + lsize - xendshift + 1),
123:             thrust::device_ptr<const PetscScalar>(xarray + lsize - xendshift - 1),
124:             thrust::counting_iterator<int>(fstart) + lsize,
125:             thrust::constant_iterator<int>(Mx),
126:             thrust::constant_iterator<PetscScalar>(hx))),
127:         ApplyStencil());
128:     }
129:     catch (char *all) {
130:       PetscPrintf(PETSC_COMM_WORLD, "Thrust is not working\n");
131:     }
132:     VecCUDARestoreArrayRead(xlocal,&xarray);
133:     VecCUDARestoreArrayWrite(f,&farray);
134:   } else {
135:     DMDAVecGetArray(da,xlocal,&xx);
136:     DMDAVecGetArray(da,f,&ff);
137:     DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);

139:     for (i=xs; i<xs+xm; i++) {
140:       if (i == 0 || i == Mx-1) ff[i] = xx[i]/hx;
141:       else ff[i] =  (2.0*xx[i] - xx[i-1] - xx[i+1])/hx - hx*PetscExpScalar(xx[i]);
142:     }
143:     DMDAVecRestoreArray(da,xlocal,&xx);
144:     DMDAVecRestoreArray(da,f,&ff);
145:   }
146:   DMRestoreLocalVector(da,&xlocal);
147:   //  VecView(x,0);printf("f\n");
148:   //  VecView(f,0);
149:   return 0;

151: }
152: PetscErrorCode ComputeJacobian(SNES snes,Vec x,Mat J,Mat B,void *ctx)
153: {
154:   DM             da = (DM) ctx;
155:   PetscInt       i,Mx,xm,xs;
156:   PetscScalar    hx,*xx;
157:   Vec            xlocal;

160:   DMDAGetInfo(da,PETSC_IGNORE,&Mx,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE);
161:   hx   = 1.0/(PetscReal)(Mx-1);
162:   DMGetLocalVector(da,&xlocal);DMGlobalToLocalBegin(da,x,INSERT_VALUES,xlocal);
163:   DMGlobalToLocalEnd(da,x,INSERT_VALUES,xlocal);
164:   DMDAVecGetArray(da,xlocal,&xx);
165:   DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);

167:   for (i=xs; i<xs+xm; i++) {
168:     if (i == 0 || i == Mx-1) {
169:       MatSetValue(J,i,i,1.0/hx,INSERT_VALUES);
170:     } else {
171:       MatSetValue(J,i,i-1,-1.0/hx,INSERT_VALUES);
172:       MatSetValue(J,i,i,2.0/hx - hx*PetscExpScalar(xx[i]),INSERT_VALUES);
173:       MatSetValue(J,i,i+1,-1.0/hx,INSERT_VALUES);
174:     }
175:   }
176:   MatAssemblyBegin(J,MAT_FINAL_ASSEMBLY);
177:   MatAssemblyEnd(J,MAT_FINAL_ASSEMBLY);
178:   DMDAVecRestoreArray(da,xlocal,&xx);
179:   DMRestoreLocalVector(da,&xlocal);
180:   return 0;
181: }



185: /*TEST

187:    build:
188:       requires: cuda

190:    testset:
191:       args: -snes_monitor_short -dm_mat_type aijcusparse -dm_vec_type cuda
192:       output_file: output/ex47cu_1.out
193:       test:
194:         suffix: 1
195:         nsize:  1
196:       test:
197:         suffix: 2
198:         nsize:  2

200: TEST*/