Drivers: hv: vmbus: Implement per-CPU mapping of relid to channel

Currently the mapping of the relID to channel is done under the protection of a
single spin lock. Starting with ws2012, each channel is bound to a specific VCPU
in the guest. Use this binding to eliminate the spin lock by setting up
per-cpu state for mapping relId to the channel.

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, 23 insertions, 1 deletions

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index df2363ea017f..7f10c151632a 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -234,6 +234,28 @@ cleanup:
         return ret;
 }
 
+/*
+ * Map the given relid to the corresponding channel based on the
+ * per-cpu list of channels that have been affinitized to this CPU.
+ * This will be used in the channel callback path as we can do this
+ * mapping in a lock-free fashion.
+ */
+static struct vmbus_channel *pcpu_relid2channel(u32 relid)
+{
+        struct vmbus_channel *channel;
+        struct vmbus_channel *found_channel  = NULL;
+        int cpu = smp_processor_id();
+        struct list_head *pcpu_head = &hv_context.percpu_list[cpu];
+
+        list_for_each_entry(channel, pcpu_head, percpu_list) {
+                if (channel->offermsg.child_relid == relid) {
+                        found_channel = channel;
+                        break;
+                }
+        }
+
+        return found_channel;
+}
 
 /*
  * relid2channel - Get the channel object given its
@@ -285,7 +307,7 @@ static void process_chn_event(u32 relid)
          * Find the channel based on this relid and invokes the
          * channel callback to process the event
          */
-        channel = relid2channel(relid);
+        channel = pcpu_relid2channel(relid);
 
         if (!channel) {
                 pr_err("channel not found for relid - %u\n", relid);