RDMA/cxgb4: Optimize CQ overflow detection

1) save the timestamp flit in the cq when we consume a CQE.

2) always compare the saved flit with the previous entry flit when
   reading the next CQE entry.  If the flits don't compare, then we
   have overflowed.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

2 files changed, 17 insertions, 12 deletions

diff --git a/drivers/infiniband/hw/cxgb4/cq.c b/drivers/infiniband/hw/cxgb4/cq.c
index 46ac00f728f3..2447f5295482 100644
--- a/drivers/infiniband/hw/cxgb4/cq.c
+++ b/drivers/infiniband/hw/cxgb4/cq.c
@@ -373,6 +373,7 @@ static void create_read_req_cqe(struct t4_wq *wq, struct t4_cqe *hw_cqe,
                                  V_CQE_SWCQE(SW_CQE(hw_cqe)) |
                                  V_CQE_OPCODE(FW_RI_READ_REQ) |
                                  V_CQE_TYPE(1));
+        read_cqe->bits_type_ts = hw_cqe->bits_type_ts;
 }
 
 /*
diff --git a/drivers/infiniband/hw/cxgb4/t4.h b/drivers/infiniband/hw/cxgb4/t4.h
index d0e8af352408..712bc5620d3e 100644
--- a/drivers/infiniband/hw/cxgb4/t4.h
+++ b/drivers/infiniband/hw/cxgb4/t4.h
@@ -434,7 +434,7 @@ struct t4_cq {
         struct c4iw_rdev *rdev;
         u64 ugts;
         size_t memsize;
-        u64 timestamp;
+        __be64 bits_type_ts;
         u32 cqid;
         u16 size; /* including status page */
         u16 cidx;
@@ -487,6 +487,7 @@ static inline void t4_swcq_consume(struct t4_cq *cq)
 
 static inline void t4_hwcq_consume(struct t4_cq *cq)
 {
+        cq->bits_type_ts = cq->queue[cq->cidx].bits_type_ts;
         cq->cidx_inc++;
         if (++cq->cidx == cq->size) {
                 cq->cidx = 0;
@@ -501,20 +502,23 @@ static inline int t4_valid_cqe(struct t4_cq *cq, struct t4_cqe *cqe)
 
 static inline int t4_next_hw_cqe(struct t4_cq *cq, struct t4_cqe **cqe)
 {
-        int ret = 0;
-        u64 bits_type_ts = be64_to_cpu(cq->queue[cq->cidx].bits_type_ts);
+        int ret;
+        u16 prev_cidx;
 
-        if (G_CQE_GENBIT(bits_type_ts) == cq->gen) {
-                *cqe = &cq->queue[cq->cidx];
-                cq->timestamp = G_CQE_TS(bits_type_ts);
-        } else if (G_CQE_TS(bits_type_ts) > cq->timestamp)
-                ret = -EOVERFLOW;
+        if (cq->cidx == 0)
+                prev_cidx = cq->size - 1;
         else
-                ret = -ENODATA;
-        if (ret == -EOVERFLOW) {
-                printk(KERN_ERR MOD "cq overflow cqid %u\n", cq->cqid);
+                prev_cidx = cq->cidx - 1;
+
+        if (cq->queue[prev_cidx].bits_type_ts != cq->bits_type_ts) {
+                ret = -EOVERFLOW;
                 cq->error = 1;
-        }
+                printk(KERN_ERR MOD "cq overflow cqid %u\n", cq->cqid);
+        } else if (t4_valid_cqe(cq, &cq->queue[cq->cidx])) {
+                *cqe = &cq->queue[cq->cidx];
+                ret = 0;
+        } else
+                ret = -ENODATA;
         return ret;
 }