Drivers: hv: vmbus: Use a round-robin algorithm for picking the outgoing channel

The current algorithm for picking an outgoing channel was not distributing
the load well. Implement a simple round-robin scheme to ensure good
distribution of the outgoing traffic.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 15 insertions, 15 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index b1e5a5fdaf7f..611789139f9b 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -350,6 +350,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
                         }
 
                         newchannel->state = CHANNEL_OPEN_STATE;
+                        channel->num_sc++;
                         if (channel->sc_creation_callback != NULL)
                                 /*
                                  * We need to invoke the sub-channel creation
@@ -862,9 +863,8 @@ cleanup:
 
 /*
  * Retrieve the (sub) channel on which to send an outgoing request.
- * When a primary channel has multiple sub-channels, we choose a
- * channel whose VCPU binding is closest to the VCPU on which
- * this call is being made.
+ * When a primary channel has multiple sub-channels, we try to
+ * distribute the load equally amongst all available channels.
  */
 struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
 {
@@ -872,11 +872,19 @@ struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
         int cur_cpu;
         struct vmbus_channel *cur_channel;
         struct vmbus_channel *outgoing_channel = primary;
-        int cpu_distance, new_cpu_distance;
+        int next_channel;
+        int i = 1;
 
         if (list_empty(&primary->sc_list))
                 return outgoing_channel;
 
+        next_channel = primary->next_oc++;
+
+        if (next_channel > (primary->num_sc)) {
+                primary->next_oc = 0;
+                return outgoing_channel;
+        }
+
         cur_cpu = hv_context.vp_index[get_cpu()];
         put_cpu();
         list_for_each_safe(cur, tmp, &primary->sc_list) {
@@ -887,18 +895,10 @@ struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
                 if (cur_channel->target_vp == cur_cpu)
                         return cur_channel;
 
-                cpu_distance = ((outgoing_channel->target_vp > cur_cpu) ?
-                                (outgoing_channel->target_vp - cur_cpu) :
-                                (cur_cpu - outgoing_channel->target_vp));
-
-                new_cpu_distance = ((cur_channel->target_vp > cur_cpu) ?
-                                (cur_channel->target_vp - cur_cpu) :
-                                (cur_cpu - cur_channel->target_vp));
-
-                if (cpu_distance < new_cpu_distance)
-                        continue;
+                if (i == next_channel)
+                        return cur_channel;
 
-                outgoing_channel = cur_channel;
+                i++;
         }
 
         return outgoing_channel;