[PATCH v7 for-next 2/2] IB/core: Read subnet_prefix in ib_query_port via cache.

[Anand Khoje <anand.a.khoje@oracle.com>]

ib_query_port() calls device->ops.query_port() to get the port
attributes. The method of querying is device driver specific.
The same function calls device->ops.query_gid() to get the GID and
extract the subnet_prefix (gid_prefix).

The GID and subnet_prefix are stored in a cache. But they do not get
read from the cache if the device is an Infiniband device. The
following change takes advantage of the cached subnet_prefix.
Testing with RDBMS has shown a significant improvement in performance
with this change.

The variable cache_is_initialized is added because ib_query_port()
gets called early in the stage when cache is not built while reading
port immutable properties.

In that case, the default GID still gets read from HCA for IB link-
layer devices.

Fixes: fad61ad ("IB/core: Add subnet prefix to port info")
Signed-off-by: Anand Khoje <anand.a.khoje@oracle.com>
Signed-off-by: Haakon Bugge <haakon.bugge@oracle.com>
---
 drivers/infiniband/core/cache.c  | 1 +
 drivers/infiniband/core/device.c | 9 +++++++++
 include/rdma/ib_verbs.h          | 1 +
 3 files changed, 11 insertions(+)

diff --git a/drivers/infiniband/core/cache.c b/drivers/infiniband/core/cache.c
index 929399e..4150043 100644
--- a/drivers/infiniband/core/cache.c
+++ b/drivers/infiniband/core/cache.c
@@ -1631,6 +1631,7 @@ int ib_cache_setup_one(struct ib_device *device)
 		err = ib_cache_update(device, p, true, true, true);
 		if (err)
 			return err;
+		device->port_data[p].cache_is_initialized = 1;
 	}
 
 	return 0;
diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
index fa20b18..e078a48 100644
--- a/drivers/infiniband/core/device.c
+++ b/drivers/infiniband/core/device.c
@@ -2063,6 +2063,15 @@ static int __ib_query_port(struct ib_device *device,
 	    IB_LINK_LAYER_INFINIBAND)
 		return 0;
 
+	if (!device->port_data[port_num].cache_is_initialized)
+		goto query_gid_from_device;
+
+	ib_get_cached_subnet_prefix(device, port_num,
+				    &port_attr->subnet_prefix);
+
+	return 0;
+
+query_gid_from_device:
 	err = device->ops.query_gid(device, port_num, 0, &gid);
 	if (err)
 		return err;
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 371df1c..e692f9b 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -2179,6 +2179,7 @@ struct ib_port_data {
 
 	spinlock_t netdev_lock;
 
+	u8 cache_is_initialized:1;
 	struct list_head pkey_list;
 
 	struct ib_port_cache cache;
-- 
1.8.3.1