From: Michael J. Ruhl <michael.j.ruhl@xxxxxxxxx>
A recent performance enhancement introduced a latency issue in the
HFI message path. The new algorithm removed a forced call send for
PIO messages and added a forced schedule event for messages larger
than the MTU.
For PIO, the schedule path can introduce thrashing that can
significantly impact the throughput for small messages.
If a message size is within the PIO threshold, always take the send
path.
Fixes: 0b79b27748cb ("IB/{hfi1, qib, rdmavt}: Schedule multi RC/UC packets instead of posting")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@xxxxxxxxx>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
---
drivers/infiniband/hw/hfi1/qp.c | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/drivers/infiniband/hw/hfi1/qp.c b/drivers/infiniband/hw/hfi1/qp.c
index 6f3bc4d..1a01624 100644
--- a/drivers/infiniband/hw/hfi1/qp.c
+++ b/drivers/infiniband/hw/hfi1/qp.c
@@ -340,6 +340,13 @@ int hfi1_setup_wqe(struct rvt_qp *qp, struct rvt_swqe *wqe, bool *call_send)
default:
break;
}
+
+ /*
+ * System latency between send and schedule is large enough that
+ * forcing call_send to true for piothreshold packets is necessary.
+ */
+ if (wqe->length <= piothreshold)
+ *call_send = true;
return 0;
}
