pml/yalla: fix yalla performance regression

It was introduced in PR https://github.com/open-mpi/ompi/pull/1228
 in particular in commit 041a6a9f53033a12d1cbf5c1af36cb16c7cdcc36.

 Original solution was using "flexible array member" called "mxm_base"
 to "fall-through" to the "mxm" send/recv member that located in the
 outer structure.

 After changing number of elements in "mxm_base" from 0 to 1 we actually
 allocating 2 mxm_req_base_t elements which leads to increased overal
 size and harms cache performance.

 It also brakes "mca_pml_yalla_check_request_state" function.

ompi/mca/pml/yalla/pml_yalla.c

@@ -688,6 +688,7 @@ int mca_pml_yalla_start(size_t count, ompi_request_t** requests)
 
     for (i = 0; i < count; ++i) {
         req = (mca_pml_yalla_base_request_t *)requests[i];
+        sreq = (mca_pml_yalla_send_request_t *)req;
 
         if ((req == NULL) || (OMPI_REQUEST_PML != req->ompi.req_type)) {
             /* Skip irrelevant requests */
@@ -696,10 +697,9 @@ int mca_pml_yalla_start(size_t count, ompi_request_t** requests)
 
         PML_YALLA_ASSERT(req->ompi.req_state != OMPI_REQUEST_INVALID);
         PML_YALLA_RESET_OMPI_REQ(&req->ompi, OMPI_REQUEST_ACTIVE);
-        PML_YALLA_RESET_PML_REQ(req);
+        PML_YALLA_RESET_PML_REQ(req, PML_YALLA_MXM_REQBASE(sreq));
 
         if (req->flags & MCA_PML_YALLA_REQUEST_FLAG_SEND) {
-            sreq = (mca_pml_yalla_send_request_t *)req;
             if (req->flags & MCA_PML_YALLA_REQUEST_FLAG_BSEND) {
                 PML_YALLA_VERBOSE(8, "start bsend request %p", (void *)sreq);
                 rc = mca_pml_yalla_bsend(&sreq->mxm);

ompi/mca/pml/yalla/pml_yalla_request.c

@@ -32,10 +32,10 @@ static inline void mca_pml_yalla_request_release(mca_pml_yalla_base_request_t *r
 }
 
 static inline int
-mca_pml_yalla_check_request_state(mca_pml_yalla_base_request_t *req)
+mca_pml_yalla_check_request_state(mca_pml_yalla_base_request_t *req, mxm_req_base_t *mxm_base)
 {
-    if (req->mxm_base->state != MXM_REQ_COMPLETED) {
-         PML_YALLA_VERBOSE(8, "request %p free called before completed", (void *)req);
+    if ( mxm_base->state != MXM_REQ_COMPLETED) {
+         PML_YALLA_VERBOSE(8, "request %p free called before completed", (void*)req);
          req->flags |= MCA_PML_YALLA_REQUEST_FLAG_FREE_CALLED;
          return 0;
     }
@@ -45,11 +45,12 @@ mca_pml_yalla_check_request_state(mca_pml_yalla_base_request_t *req)
 
 static int mca_pml_yalla_send_request_free(ompi_request_t **request)
 {
-    mca_pml_yalla_base_request_t *req = (mca_pml_yalla_base_request_t*)(*request);
+    mca_pml_yalla_send_request_t *sreq = (mca_pml_yalla_send_request_t*)(*request);
+    mca_pml_yalla_base_request_t *req = (mca_pml_yalla_base_request_t*)sreq;
 
     PML_YALLA_VERBOSE(9, "free send request *%p=%p", (void *)request, (void *)*request);
 
-    if (mca_pml_yalla_check_request_state(req)) {
+    if (mca_pml_yalla_check_request_state(req, PML_YALLA_MXM_REQBASE(sreq))) {
         mca_pml_yalla_request_release(req, &ompi_pml_yalla.send_reqs);
     }
 
@@ -84,11 +85,12 @@ static int mca_pml_yalla_send_request_cancel(ompi_request_t *request, int flag)
 
 static int mca_pml_yalla_recv_request_free(ompi_request_t **request)
 {
-    mca_pml_yalla_base_request_t *req = (mca_pml_yalla_base_request_t*)(*request);
+    mca_pml_yalla_recv_request_t *rreq = (mca_pml_yalla_recv_request_t*)(*request);
+    mca_pml_yalla_base_request_t *req = (mca_pml_yalla_base_request_t*)rreq;
 
     PML_YALLA_VERBOSE(9, "free receive request *%p=%p", (void *)request, (void *)*request);
 
-    if (mca_pml_yalla_check_request_state(req)) {
+    if (mca_pml_yalla_check_request_state(req, PML_YALLA_MXM_REQBASE(rreq))) {
         mca_pml_yalla_request_release(req, &ompi_pml_yalla.recv_reqs);
     }
 

ompi/mca/pml/yalla/pml_yalla_request.h

@@ -25,15 +25,6 @@ struct pml_yalla_base_request {
     ompi_request_t               ompi;
     mca_pml_yalla_convertor_t    *convertor;
     int                          flags;
-    /* overlaps with base of send/recv
-     * In ISO C90, you would have to give contents a length of 1,
-     * which means either you waste space or complicate the argument to malloc.
-     * Note:
-     *  - 1 was the portable way to go, though it was rather strange
-     *  - 0 was better at indicating intent, but not legal as far as
-     *  the Standard was concerned and supported as an extension by some compilers (including gcc)
-     */
-    mxm_req_base_t               mxm_base[1];
 };
 
 struct pml_yalla_send_request {
@@ -58,6 +49,8 @@ OBJ_CLASS_DECLARATION(mca_pml_yalla_recv_request_t);
 
 void mca_pml_yalla_init_reqs(void);
 
+#define PML_YALLA_MXM_REQBASE( x ) ( &((x)->mxm.base) )
+
 #define PML_YALLA_RESET_OMPI_REQ(_ompi_req, _state) \
     { \
         (_ompi_req)->req_state = _state; \
@@ -72,9 +65,9 @@ void mca_pml_yalla_init_reqs(void);
         OBJ_RETAIN(_comm); \
     }
 
-#define PML_YALLA_RESET_PML_REQ(_pml_req) \
+#define PML_YALLA_RESET_PML_REQ(_pml_req, mxm_base) \
     { \
-        (_pml_req)->mxm_base[0].state = MXM_REQ_NEW; \
+        mxm_base->state = MXM_REQ_NEW; \
         PML_YALLA_RESET_PML_REQ_DATA(_pml_req); \
     }