Added explanation for kernels

examples/README.md

@@ -5,18 +5,19 @@ The used compilers were Intel Parallel Studio 19.0up05 and GNU 9.1.0 i
 
 To analyze the kernels with OSACA, run
 ```
-osaca --arch ARCH filepath
+osaca --arch ARCH FILE
 ```
 While all Zen and TX2 kernels use the comment-style OSACA markers, the kernels for Intel Cascade Lake (*.csx.*.s) use the byte markers to be able to be analyzed by IACA as well.
 For this use
 ```
-iaca -arch SKX filepath
+gcc -c FILE.s
+iaca -arch SKX FILE.o
 ```
 
 ------------
-The kernels will be explained briefly in the following.
+The kernels currently contained in the examples are shown briefly in the following.
 
-### Copy
+### Copy (`copy/`)
 ```c
 double * restrict a, * restrict b;
 
@@ -25,19 +26,89 @@ for(long i=0; i < size; ++i){
 }
 ```
 
-### Vector add
+### Vector add (`add/`)
+```c
+double * restrict a, * restrict b, * restrict c;
 
-### Vector update
+for(long i=0; i < size; ++i){
+    a[i] = b[i] + c[i];
+}
+```
 
-### Sum reduction
+### Vector update (`update/`)
+```c
+double * restrict a;
 
-### DAXPY
+for(long i=0; i < size; ++i){
+    a[i] = scale * a[i];
+}
+```
 
-### STREAM triad
+### Sum reduction (`sum_reduction/`)
+```c
+double * restrict a;
 
-### Schönauer triad
+for(long i=0; i < size; ++i){
+    scale = scale + a[i];
+}
+```
+For this kernel we noticed an overlap of the loop bodies when using gcc with `-Ofast` flag (see this [blog post](https://blogs.fau.de/hager/archives/7658) for more information).
+We therefore compiled all gcc version additionally with `-O3` flag instead.
+These versions are named accordingly.
 
-### Gauss-Seidel method
+### DAXPY (`daxpy/`)
+```c
+double * restrict a, * restrict b;
 
-### Jacobi 2D
+for(long i=0; i < size; ++i){
+    a[i] = a[i] + scale * b[i];
+}
+```
 
+### STREAM triad (`triad/`)
+```c
+double * restrict a, * restrict b, * restrict c;
+
+for(long i=0; i < size; ++i){
+    a[i] = b[i] + scale * c[i];
+}
+```
+
+### Schönauer triad (`striad/`)
+```c
+double * restrict a, * restrict b, * restrict c, *  restrict d;
+
+for(long i=0; i < size; ++i){
+    a[i] = b[i] + c[i] * d[i];
+}
+```
+
+### Gauss-Seidel method (`gs/`)
+```c
+double ** restrict a;
+
+for(long k=1; k < size_k-1; ++k){
+  for(long i=1; i < size_i-1; ++i){
+    a[k][i] = scale * (
+      a[k][i-1] + a[k+1][i]
+      + a[k][i+1] + a[k-1][i]
+    );
+  }
+}
+```
+
+### Jacobi 2D (`j2d/`)
+```c
+double ** restrict a, ** restrict b;
+
+for(long k=1; k < size_k-1; ++k){
+  for(long i=1; i < size_i-1; ++i){
+    a[k][i] = 0.25 * (
+      b[k][i-1] + b[k+1][i]
+      + b[k][i+1] + b[k-1][i]
+    );
+  }
+}
+```
+For this kernel we noticed a discrepancy between measurements and predcitions especially when using AVX-512 instructions.
+We therefore compiled the x86 kernels additionally with AVX/SSE instruction and marekd those kernels accordingly.