Drivers: hv: Eliminate the channel spinlock in the callback path

By ensuring that we set the callback handler to NULL in the channel close
path on the same CPU that the channel is bound to, we can eliminate this lock
acquisition and release in a performance critical path.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index fa920469bf10..6f7fdd9a7e77 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -365,7 +365,7 @@ static u32  next_vp;
  * performance critical channels (IDE, SCSI and Network) will be uniformly
  * distributed across all available CPUs.
  */
-static u32 get_vp_index(uuid_le *type_guid)
+static void init_vp_index(struct vmbus_channel *channel, uuid_le *type_guid)
 {
         u32 cur_cpu;
         int i;
@@ -387,10 +387,13 @@ static u32 get_vp_index(uuid_le *type_guid)
                  * Also if the channel is not a performance critical
                  * channel, bind it to cpu 0.
                  */
-                return 0;
+                channel->target_cpu = 0;
+                channel->target_vp = 0;
+                return;
         }
         cur_cpu = (++next_vp % max_cpus);
-        return hv_context.vp_index[cur_cpu];
+        channel->target_cpu = cur_cpu;
+        channel->target_vp = hv_context.vp_index[cur_cpu];
 }
 
 /*
@@ -438,7 +441,7 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
                                 offer->connection_id;
         }
 
-        newchannel->target_vp = get_vp_index(&offer->offer.if_type);
+        init_vp_index(newchannel, &offer->offer.if_type);
 
         memcpy(&newchannel->offermsg, offer,
                sizeof(struct vmbus_channel_offer_channel));