[Beignet] [PATCH V2] When local_work_size is null, try to choose a local_work_size.

[Yang Rong]

After fix all found fails when local_work_size is not 1, re-enalbe it to
improve performance.

V2: refine to skip some useless loop.
Signed-off-by: Yang Rong <rong.r.yang at intel.com>
---
 src/cl_api.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/cl_api.c b/src/cl_api.c
index 405a41a..2a6f8ce 100644
--- a/src/cl_api.c
+++ b/src/cl_api.c
@@ -2472,13 +2472,20 @@ clEnqueueNDRangeKernel(cl_command_queue  command_queue,
   if (local_work_size != NULL) {
     for (i = 0; i < work_dim; ++i)
       fixed_local_sz[i] = local_work_size[i];
-  } /*else {
-    for (i = 0; i< work_dim; i++)
-      for (j = 64; j > 1; j--) {   //check from 64?
-        if (global_work_size[i] % j == 0) //global_work_size always non null
+  } else {
+    uint j, maxDimSize = 64 /* from 64? */, maxGroupSize = 256; //MAX_WORK_GROUP_SIZE may too large
+    for (i = 0; i< work_dim; i++) {
+      for (j = maxDimSize; j > 1; j--) {
+        if (global_work_size[i] % j == 0 && j <= maxGroupSize) {
           fixed_local_sz[i] = j;
+          maxGroupSize = maxGroupSize /j;
+          maxDimSize = maxGroupSize > maxDimSize ? maxDimSize : maxGroupSize;
+          break;  //choose next work_dim
+        }
       }
-  } */
+    }
+  }
+
   if (global_work_size != NULL)
     for (i = 0; i < work_dim; ++i)
       fixed_global_sz[i] = global_work_size[i];
-- 
1.8.3.2