[Qemu-devel] [PATCH 03/10] hw/rdma: Warn when too many consecutive poll CQ triggered on an empty CQ

[Yuval Shaia <yuval.shaia@oracle.com>]

To protect against CPU over utilization when guest performs unneeded
busy waiting loop on an empty CQ.

Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
---
 hw/rdma/rdma_backend.c      | 11 +++++++----
 hw/rdma/rdma_backend.h      |  2 +-
 hw/rdma/rdma_rm.c           |  1 +
 hw/rdma/rdma_rm_defs.h      |  6 +++++-
 hw/rdma/vmw/pvrdma_qp_ops.c | 24 +++++++++++++++++++++++-
 5 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/hw/rdma/rdma_backend.c b/hw/rdma/rdma_backend.c
index 2f6372f8f0..b7d6afb5da 100644
--- a/hw/rdma/rdma_backend.c
+++ b/hw/rdma/rdma_backend.c
@@ -64,9 +64,9 @@ static inline void complete_work(enum ibv_wc_status status, uint32_t vendor_err,
     comp_handler(ctx, &wc);
 }
 
-static void rdma_poll_cq(RdmaDeviceResources *rdma_dev_res, struct ibv_cq *ibcq)
+static int rdma_poll_cq(RdmaDeviceResources *rdma_dev_res, struct ibv_cq *ibcq)
 {
-    int i, ne;
+    int i, ne, total_ne = 0;
     BackendCtx *bctx;
     struct ibv_wc wc[2];
 
@@ -76,6 +76,7 @@ static void rdma_poll_cq(RdmaDeviceResources *rdma_dev_res, struct ibv_cq *ibcq)
         trace_rdma_poll_cq(ne, ibcq);
 
         for (i = 0; i < ne; i++) {
+            total_ne++;
             bctx = rdma_rm_get_cqe_ctx(rdma_dev_res, wc[i].wr_id);
             if (unlikely(!bctx)) {
                 rdma_error_report("No matching ctx for req %"PRId64,
@@ -93,6 +94,8 @@ static void rdma_poll_cq(RdmaDeviceResources *rdma_dev_res, struct ibv_cq *ibcq)
     if (ne < 0) {
         rdma_error_report("ibv_poll_cq fail, rc=%d, errno=%d", ne, errno);
     }
+
+    return total_ne;
 }
 
 static void *comp_handler_thread(void *arg)
@@ -267,9 +270,9 @@ int rdma_backend_query_port(RdmaBackendDev *backend_dev,
     return 0;
 }
 
-void rdma_backend_poll_cq(RdmaDeviceResources *rdma_dev_res, RdmaBackendCQ *cq)
+int rdma_backend_poll_cq(RdmaDeviceResources *rdma_dev_res, RdmaBackendCQ *cq)
 {
-    rdma_poll_cq(rdma_dev_res, cq->ibcq);
+    return rdma_poll_cq(rdma_dev_res, cq->ibcq);
 }
 
 static GHashTable *ah_hash;
diff --git a/hw/rdma/rdma_backend.h b/hw/rdma/rdma_backend.h
index 5114c90e67..36305cd148 100644
--- a/hw/rdma/rdma_backend.h
+++ b/hw/rdma/rdma_backend.h
@@ -85,7 +85,7 @@ void rdma_backend_destroy_mr(RdmaBackendMR *mr);
 int rdma_backend_create_cq(RdmaBackendDev *backend_dev, RdmaBackendCQ *cq,
                            int cqe);
 void rdma_backend_destroy_cq(RdmaBackendCQ *cq);
-void rdma_backend_poll_cq(RdmaDeviceResources *rdma_dev_res, RdmaBackendCQ *cq);
+int rdma_backend_poll_cq(RdmaDeviceResources *rdma_dev_res, RdmaBackendCQ *cq);
 
 int rdma_backend_create_qp(RdmaBackendQP *qp, uint8_t qp_type,
                            RdmaBackendPD *pd, RdmaBackendCQ *scq,
diff --git a/hw/rdma/rdma_rm.c b/hw/rdma/rdma_rm.c
index 64c6ea1a4e..1ba77ac42c 100644
--- a/hw/rdma/rdma_rm.c
+++ b/hw/rdma/rdma_rm.c
@@ -261,6 +261,7 @@ int rdma_rm_alloc_cq(RdmaDeviceResources *dev_res, RdmaBackendDev *backend_dev,
     if (!cq) {
         return -ENOMEM;
     }
+    atomic_set(&cq->missing_cqe, 0);
 
     cq->opaque = opaque;
     cq->notify = CNT_CLEAR;
diff --git a/hw/rdma/rdma_rm_defs.h b/hw/rdma/rdma_rm_defs.h
index 0ba61d1838..08692e87d4 100644
--- a/hw/rdma/rdma_rm_defs.h
+++ b/hw/rdma/rdma_rm_defs.h
@@ -34,7 +34,9 @@
 #define MAX_QP_INIT_RD_ATOM   16
 #define MAX_AH                64
 
-#define MAX_RM_TBL_NAME 16
+#define MAX_RM_TBL_NAME             16
+#define MAX_CONSEQ_EMPTY_POLL_CQ    2048 /* considered as error above this */
+
 typedef struct RdmaRmResTbl {
     char name[MAX_RM_TBL_NAME];
     QemuMutex lock;
@@ -59,6 +61,8 @@ typedef struct RdmaRmCQ {
     RdmaBackendCQ backend_cq;
     void *opaque;
     CQNotificationType notify;
+    int missing_cqe;
+    int conseq_empty_poll;
 } RdmaRmCQ;
 
 /* MR (DMA region) */
diff --git a/hw/rdma/vmw/pvrdma_qp_ops.c b/hw/rdma/vmw/pvrdma_qp_ops.c
index 16db726dac..5d650a4943 100644
--- a/hw/rdma/vmw/pvrdma_qp_ops.c
+++ b/hw/rdma/vmw/pvrdma_qp_ops.c
@@ -60,6 +60,8 @@ static int pvrdma_post_cqe(PVRDMADev *dev, uint32_t cq_handle,
         return -EINVAL;
     }
 
+    atomic_dec(&cq->missing_cqe);
+
     ring = (PvrdmaRing *)cq->opaque;
 
     /* Step #1: Put CQE on CQ ring */
@@ -141,12 +143,15 @@ void pvrdma_qp_send(PVRDMADev *dev, uint32_t qp_handle)
     PvrdmaRing *ring;
     int sgid_idx;
     union ibv_gid *sgid;
+    RdmaRmCQ *cq;
 
     qp = rdma_rm_get_qp(&dev->rdma_dev_res, qp_handle);
     if (unlikely(!qp)) {
         return;
     }
 
+    cq = rdma_rm_get_cq(&dev->rdma_dev_res, qp->send_cq_handle);
+
     ring = (PvrdmaRing *)qp->opaque;
 
     wqe = (struct PvrdmaSqWqe *)pvrdma_ring_next_elem_read(ring);
@@ -186,6 +191,7 @@ void pvrdma_qp_send(PVRDMADev *dev, uint32_t qp_handle)
             continue;
         }
 
+        atomic_inc(&cq->missing_cqe);
         rdma_backend_post_send(&dev->backend_dev, &qp->backend_qp, qp->qp_type,
                                (struct ibv_sge *)&wqe->sge[0], wqe->hdr.num_sge,
                                sgid_idx, sgid,
@@ -204,12 +210,15 @@ void pvrdma_qp_recv(PVRDMADev *dev, uint32_t qp_handle)
     RdmaRmQP *qp;
     PvrdmaRqWqe *wqe;
     PvrdmaRing *ring;
+    RdmaRmCQ *cq;
 
     qp = rdma_rm_get_qp(&dev->rdma_dev_res, qp_handle);
     if (unlikely(!qp)) {
         return;
     }
 
+    cq = rdma_rm_get_cq(&dev->rdma_dev_res, qp->recv_cq_handle);
+
     ring = &((PvrdmaRing *)qp->opaque)[1];
 
     wqe = (struct PvrdmaRqWqe *)pvrdma_ring_next_elem_read(ring);
@@ -231,6 +240,7 @@ void pvrdma_qp_recv(PVRDMADev *dev, uint32_t qp_handle)
             continue;
         }
 
+        atomic_inc(&cq->missing_cqe);
         rdma_backend_post_recv(&dev->backend_dev, &dev->rdma_dev_res,
                                &qp->backend_qp, qp->qp_type,
                                (struct ibv_sge *)&wqe->sge[0], wqe->hdr.num_sge,
@@ -245,11 +255,23 @@ void pvrdma_qp_recv(PVRDMADev *dev, uint32_t qp_handle)
 void pvrdma_cq_poll(RdmaDeviceResources *dev_res, uint32_t cq_handle)
 {
     RdmaRmCQ *cq;
+    int polled;
 
     cq = rdma_rm_get_cq(dev_res, cq_handle);
     if (!cq) {
         return;
     }
 
-    rdma_backend_poll_cq(dev_res, &cq->backend_cq);
+    polled = rdma_backend_poll_cq(dev_res, &cq->backend_cq);
+    if (!polled) {
+        if (cq->conseq_empty_poll == MAX_CONSEQ_EMPTY_POLL_CQ) {
+            rdma_warn_report("%d consequtive empty polls from CQ %d, missing cqe %d",
+                             cq->conseq_empty_poll, cq_handle,
+                             atomic_read(&cq->missing_cqe));
+            cq->conseq_empty_poll = 0;
+        }
+        cq->conseq_empty_poll++;
+    } else {
+        cq->conseq_empty_poll = 0;
+    }
 }
-- 
2.17.2