OpenACC 书上的范例代码（Jacobi 迭代），part 3
▶ 使用Jacobi 迭代求泊松方程的数值解
● 使用 data 构件，强行要求 u0 仅拷入和拷出 GPU 各一次，u1 仅拷入GPU 一次
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <openacc.h> #if defined(_WIN32) || defined(_WIN64)
#include <C:\Program Files\PGI\win64\19.4\include\wrap\sys\timeb.h>
#define timestruct clock_t
#define gettime(a) (*(a) = clock())
#define usec(t1,t2) (t2 - t1)
#else
#include <sys/time.h>
#define gettime(a) gettimeofday(a, NULL)
#define usec(t1,t2) (((t2).tv_sec - (t1).tv_sec) * 1000000 + (t2).tv_usec - (t1).tv_usec)
typedef struct timeval timestruct;
#endif inline float uval(float x, float y)
{
return x * x + y * y;
} int main()
{
const int row = , col = ;
const float height = 1.0, width = 2.0;
const float hx = height / row, wy = width / col;
const float fij = -4.0f;
const float hx2 = hx * hx, wy2 = wy * wy, c1 = hx2 * wy2, c2 = 1.0f / (2.0 * (hx2 + wy2));
const int maxIter = ;
const int colPlus = col + ; float *restrict u0 = (float *)malloc(sizeof(float)*(row + )*colPlus);
float *restrict u1 = (float *)malloc(sizeof(float)*(row + )*colPlus);
float *utemp = NULL; // 初始化
for (int ix = ; ix <= row; ix++)
{
u0[ix*colPlus + ] = u1[ix*colPlus + ] = uval(ix * hx, 0.0f);
u0[ix*colPlus + col] = u1[ix*colPlus + col] = uval(ix*hx, col * wy);
}
for (int jy = ; jy <= col; jy++)
{
u0[jy] = u1[jy] = uval(0.0f, jy * wy);
u0[row*colPlus + jy] = u1[row*colPlus + jy] = uval(row*hx, jy * wy);
}
for (int ix = ; ix < row; ix++)
{
for (int jy = ; jy < col; jy++)
u0[ix*colPlus + jy] = 0.0f;
} // 计算
timestruct t1, t2;
acc_init(acc_device_nvidia);
gettime(&t1);
#pragma acc data copy(u0[0:(row + 1) * colPlus]) copyin(u1[0:(row + 1) * colPlus]) // 循环外侧添加 data 构件，跨迭代（内核）构造数据空间
{
for (int iter = ; iter < maxIter; iter++)
{
#pragma acc kernels present(u0[0:((row + 1) * colPlus)], u1[0:((row + 1) * colPlus)]) // 每次调用内核时声明 u0 和 u1 已经存在，不要再拷贝
{
#pragma acc loop independent
for (int ix = ; ix < row; ix++)
{
#pragma acc loop independent
for (int jy = ; jy < col; jy++)
{
u1[ix*colPlus + jy] = (c1*fij + wy2 * (u0[(ix - )*colPlus + jy] + u0[(ix + )*colPlus + jy]) + \
hx2 * (u0[ix*colPlus + jy - ] + u0[ix*colPlus + jy + ])) * c2;
}
}
}
utemp = u0, u0 = u1, u1 = utemp;
}
}
gettime(&t2); long long timeElapse = usec(t1, t2);
#if defined(_WIN32) || defined(_WIN64)
printf("\nElapsed time: %13ld ms.\n", timeElapse);
#else
printf("\nElapsed time: %13ld us.\n", timeElapse);
#endif
free(u0);
free(u1);
acc_shutdown(acc_device_nvidia);
//getchar();
return ;
}
● 输出结果，win10 中运行结果，关闭 PGI_ACC_NOTIFY 后可以达到 67 ms
D:\Code\OpenACC>pgcc main.c -o main.exe -c99 -Minfo -acc
main:
, Memory zero idiom, loop replaced by call to __c_mzero4
, Generating copy(u0[:colPlus*(row+)])
Generating copyin(u1[:colPlus*(row+)])
, Generating present(u1[:colPlus*(row+)],u0[:colPlus*(row+)])
, Loop is parallelizable
, Loop is parallelizable
Generating Tesla code
, #pragma acc loop gang, vector(4) /* blockIdx.y threadIdx.y */
, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */
, FMA (fused multiply-add) instruction(s) generated
uval:
, FMA (fused multiply-add) instruction(s) generated D:\Code\OpenACC>main.exe
launch CUDA kernel file=D:\Code\OpenACC\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 ... launch CUDA kernel file=D:\Code\OpenACC\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 Elapsed time: ms.
● nvvp 结果，可见大部分时间都花在了初始化设备上，计算用时已经比较少了，拷贝用时更少，只有开头和结尾有一点
● 输出结果，Ubuntu 中运行结果，含开启 PGI_ACC_TIME 的数据
cuan@CUAN:~$ pgcc data.c -o data.exe -c99 -Minfo -acc
main:
, Memory zero idiom, loop replaced by call to __c_mzero4
, Generating copy(u0[:colPlus*(row+)])
Generating copyin(u1[:colPlus*(row+)])
, Generating present(utemp[:],u1[:colPlus*(row+)],u0[:colPlus*(row+)])
FMA (fused multiply-add) instruction(s) generated
, Loop is parallelizable
, Loop is parallelizable
Generating Tesla code
, #pragma acc loop gang, vector(4) /* blockIdx.y threadIdx.y */
, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */
uval:
, FMA (fused multiply-add) instruction(s) generated
cuan@CUAN:~$ ./data.exe
launch CUDA kernel file=/home/cuan/data.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 ... launch CUDA kernel file=/home/cuan/data.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 Elapsed time: us. Accelerator Kernel Timing data
/home/cuan/data.c
main NVIDIA devicenum=
time(us): ,
: data region reached times
: data copyin transfers:
device time(us): total=, max=, min=, avg=,
: data copyout transfers:
device time(us): total=, max=, min= avg=
: data region reached times
: compute region reached times
: kernel launched times
grid: [32x1024] block: [32x4]
device time(us): total=, max= min= avg=
elapsed time(us): total=, max=, min= avg=
● 将 tempp 放到了更里一层循环，报运行时错误 715 或 719，参考【https://stackoverflow.com/questions/41366915/openacc-create-data-while-running-inside-a-kernels】，大意是关于内存泄露
D:\Code\OpenACC>main.exe
launch CUDA kernel file=D:\Code\OpenACC\OpenACCProject\OpenACCProject\main.c function=main
line=69 device=0 threadid=1 num_gangs=32768 num_workers=4 vector_length=32 grid=32x1024 block=32x4
launch CUDA kernel file=D:\Code\OpenACC\OpenACCProject\OpenACCProject\main.c function=main
line=74 device=0 threadid=1 num_gangs=1 num_workers=1 vector_length=1 grid=1 block=1
call to cuStreamSynchronize returned error 715: Illegal instruction call to cuMemFreeHost returned error 715: Illegal instruction D:\Code\OpenACC>main.exe
launch CUDA kernel file=D:\Code\OpenACC\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4
launch CUDA kernel file=D:\Code\OpenACC\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid= block=
Failing in Thread:
call to cuStreamSynchronize returned error : Launch failed (often invalid pointer dereference) Failing in Thread:
call to cuMemFreeHost returned error : Launch failed (often invalid pointer dereference)
● 尝试 在 data 构件中添加 create(utemp) 或在交换指针的位置临时定义 float *utemp 都会报运行时错误 700
D:\Code\OpenACC>main.exe
launch CUDA kernel file=D:\Code\OpenACC\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4
launch CUDA kernel file=D:\Code\OpenACC\main.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid= block=
Failing in Thread:
call to cuStreamSynchronize returned error : Illegal address during kernel execution Failing in Thread:
call to cuMemFreeHost returned error : Illegal address during kernel execution
▶ 恢复错误控制，添加 reduction 导语用来计量改进量
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <openacc.h> #if defined(_WIN32) || defined(_WIN64)
#include <C:\Program Files\PGI\win64\19.4\include\wrap\sys\timeb.h>
#define timestruct clock_t
#define gettime(a) (*(a) = clock())
#define usec(t1,t2) (t2 - t1)
#else
#include <sys/time.h>
#define gettime(a) gettimeofday(a, NULL)
#define usec(t1,t2) (((t2).tv_sec - (t1).tv_sec) * 1000000 + (t2).tv_usec - (t1).tv_usec)
typedef struct timeval timestruct; #define max(x,y) ((x) > (y) ? (x) : (y))
#endif inline float uval(float x, float y)
{
return x * x + y * y;
} int main()
{
const int row = , col = ;
const float height = 1.0, width = 2.0;
const float hx = height / row, wy = width / col;
const float fij = -4.0f;
const float hx2 = hx * hx, wy2 = wy * wy, c1 = hx2 * wy2, c2 = 1.0f / (2.0 * (hx2 + wy2)), errControl = 0.0f;
const int maxIter = ;
const int colPlus = col + ; float *restrict u0 = (float *)malloc(sizeof(float)*(row + )*colPlus);
float *restrict u1 = (float *)malloc(sizeof(float)*(row + )*colPlus);
float *utemp = NULL; // 初始化
for (int ix = ; ix <= row; ix++)
{
u0[ix*colPlus + ] = u1[ix*colPlus + ] = uval(ix * hx, 0.0f);
u0[ix*colPlus + col] = u1[ix*colPlus + col] = uval(ix*hx, col * wy);
}
for (int jy = ; jy <= col; jy++)
{
u0[jy] = u1[jy] = uval(0.0f, jy * wy);
u0[row*colPlus + jy] = u1[row*colPlus + jy] = uval(row*hx, jy * wy);
}
for (int ix = ; ix < row; ix++)
{
for (int jy = ; jy < col; jy++)
u0[ix*colPlus + jy] = 0.0f;
} // 计算
timestruct t1, t2;
acc_init(acc_device_nvidia);
gettime(&t1);
#pragma acc data copy(u0[0:(row + 1) * colPlus]) copyin(u1[0:(row + 1) * colPlus])
{
for (int iter = ; iter < maxIter; iter++)
{
float uerr = 0.0f; // uerr 要放到前面，否则离开代码块数据未定义，书上这里是错的
#pragma acc kernels present(u0[0:(row + 1) * colPlus]) present(u1[0:(row + 1) * colPlus])
{
#pragma acc loop independent reduction(max:uerr) // 添加 reduction 语句统计改进量
for (int ix = ; ix < row; ix++)
{
for (int jy = ; jy < col; jy++)
{
u1[ix*colPlus + jy] = (c1*fij + wy2 * (u0[(ix - )*colPlus + jy] + u0[(ix + )*colPlus + jy]) + \
hx2 * (u0[ix*colPlus + jy - ] + u0[ix*colPlus + jy + ])) * c2;
uerr = max(uerr, fabs(u0[ix * colPlus + jy] - u1[ix * colPlus + jy]));
}
}
}
printf("\niter = %d, uerr = %e\n", iter, uerr);
if (uerr < errControl)
break;
utemp = u0, u0 = u1, u1 = utemp;
}
}
gettime(&t2); long long timeElapse = usec(t1, t2);
#if defined(_WIN32) || defined(_WIN64)
printf("\nElapsed time: %13ld ms.\n", timeElapse);
#else
printf("\nElapsed time: %13ld us.\n", timeElapse);
#endif
free(u0);
free(u1);
acc_shutdown(acc_device_nvidia);
//getchar();
return ;
}
● 输出结果，win10 相比没有错误控制的情形整整慢了一倍，nvvp 没有明显变化，不放上来了
D:\Code\OpenACC>pgcc main.c -o main.exe -c99 -Minfo -acc
main:
, Memory zero idiom, loop replaced by call to __c_mzero4
, Generating copy(u0[:colPlus*(row+)])
Generating copyin(u1[:colPlus*(row+)])
, Generating present(u0[:colPlus*(row+)])
Generating implicit copy(uerr)
Generating present(u1[:colPlus*(row+)])
, Loop is parallelizable
, Loop is parallelizable
Generating Tesla code
, #pragma acc loop gang, vector(4) /* blockIdx.y threadIdx.y */
, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */
Generating reduction(max:uerr) // 多了 reduction 的信息
, FMA (fused multiply-add) instruction(s) generated
uval:
, FMA (fused multiply-add) instruction(s) generated D:\Code\OpenACC>main.exe iter = , uerr = 2.496107e+00 ... iter = , uerr = 2.202189e-02 Elapsed time: ms.
● 输出结果，Unubtu
cuan@CUAN:~$ pgcc data+reduction.c -o data+reduction.exe -c99 -Minfo -acc
main:
, Memory zero idiom, loop replaced by call to __c_mzero4
, Generating copyin(u1[:colPlus*(row+)])
Generating copy(u0[:colPlus*(row+)])
, FMA (fused multiply-add) instruction(s) generated
, Generating present(u0[:colPlus*(row+)])
Generating implicit copy(uerr)
Generating present(u1[:colPlus*(row+)])
, Loop is parallelizable
, Loop is parallelizable
Generating Tesla code
, #pragma acc loop gang, vector(4) /* blockIdx.y threadIdx.y */
, #pragma acc loop gang, vector(32) /* blockIdx.x threadIdx.x */
Generating reduction(max:uerr)
uval:
, FMA (fused multiply-add) instruction(s) generated
cuan@CUAN:~$ ./data+reduction.exe
launch CUDA kernel file=/home/cuan/data+reduction.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 shared memory=
launch CUDA kernel file=/home/cuan/data+reduction.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid= block= shared memory= iter = , uerr = 2.496107e+00
launch CUDA kernel file=/home/cuan/data+reduction.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 shared memory=
launch CUDA kernel file=/home/cuan/data+reduction.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid= block= shared memory= ... iter = , uerr = 2.214956e-02
launch CUDA kernel file=/home/cuan/data+reduction.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid=32x1024 block=32x4 shared memory=
launch CUDA kernel file=/home/cuan/data+reduction.c function=main line= device= threadid= num_gangs= num_workers= vector_length= grid= block= shared memory= iter = , uerr = 2.202189e-02 Elapsed time: us. Accelerator Kernel Timing data
/home/cuan/data+reduction.c
main NVIDIA devicenum=
time(us): ,
: data region reached times
: data copyin transfers:
device time(us): total=, max=, min=, avg=,
: data copyout transfers:
device time(us): total=, max=, min= avg=
: compute region reached times
: kernel launched times
grid: [32x1024] block: [32x4]
device time(us): total=, max= min= avg=
elapsed time(us): total=, max=, min= avg=
: reduction kernel launched times
grid: [] block: []
device time(us): total=, max= min= avg=
elapsed time(us): total=, max=, min= avg=
: data region reached times
: data copyin transfers:
device time(us): total= max= min= avg=
: data copyout transfers:
device time(us): total= max= min= avg=
▶ 尝试在计算的循环导语上加上 collapse(2) 子句，意思是合并两个较小的循环为一个较大的循环。发现效果不显著，不放上来了
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