IB/qib: Reduce sdma_lock contention

Profiling has shown that sdma_lock is proving a bottleneck for
performance. The situations include:
 - RDMA reads when krcvqs > 1
 - post sends from multiple threads

For RDMA read the current global qib_wq mechanism runs on all CPUs
and contends for the sdma_lock when multiple RMDA read requests are
fielded on differenct CPUs. For post sends, the direct call to
qib_do_send() from multiple threads causes the contention.

Since the sdma mechanism is per port, this fix converts the existing
workqueue to a per port single thread workqueue to reduce the lock
contention in the RDMA read case, and for any other case where the QP
is scheduled via the workqueue mechanism from more than 1 CPU.

For the post send case, This patch modifies the post send code to test
for a non empty sdma engine.  If the sdma is not idle the (now single
thread) workqueue will be used to trigger the send engine instead of
the direct call to qib_do_send().

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/infiniband/hw/qib/qib.h b/drivers/infiniband/hw/qib/qib.h
index 7e62f4137148..cbe577151457 100644
--- a/drivers/infiniband/hw/qib/qib.h
+++ b/drivers/infiniband/hw/qib/qib.h
@@ -1,8 +1,8 @@
 #ifndef _QIB_KERNEL_H
 #define _QIB_KERNEL_H
 /*
- * Copyright (c) 2006, 2007, 2008, 2009, 2010 QLogic Corporation.
- * All rights reserved.
+ * Copyright (c) 2012 Intel Corporation.  All rights reserved.
+ * Copyright (c) 2006 - 2012 QLogic Corporation. All rights reserved.
  * Copyright (c) 2003, 2004, 2005, 2006 PathScale, Inc. All rights reserved.
  *
  * This software is available to you under a choice of one of two
@@ -544,6 +544,7 @@ struct qib_pportdata {
 
         /* read mostly */
         struct qib_sdma_desc *sdma_descq;
+        struct workqueue_struct *qib_wq;
         struct qib_sdma_state sdma_state;
         dma_addr_t       sdma_descq_phys;
         volatile __le64 *sdma_head_dma; /* DMA'ed by chip */
@@ -1267,6 +1268,11 @@ int qib_sdma_verbs_send(struct qib_pportdata *, struct qib_sge_state *,
 /* ppd->sdma_lock should be locked before calling this. */
 int qib_sdma_make_progress(struct qib_pportdata *dd);
 
+static inline int qib_sdma_empty(const struct qib_pportdata *ppd)
+{
+        return ppd->sdma_descq_added == ppd->sdma_descq_removed;
+}
+
 /* must be called under qib_sdma_lock */
 static inline u16 qib_sdma_descq_freecnt(const struct qib_pportdata *ppd)
 {