Drivers: hv: vmbus: distribute subchannels among all vcpus

Primary channels are distributed evenly across all vcpus we have. When the host
asks us to create subchannels it usually makes us num_cpus-1 offers and we are
supposed to distribute the work evenly among the channel itself and all its
subchannels. Make sure they are all assigned to different vcpus.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 655c0a09c9022dbdd0d54259052a36fc62960ea4..1f1417d19c7eb8b88cdb9b01ddbd6801cbfd2a8e 100644 (file)
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -387,6 +387,8 @@ static void init_vp_index(struct vmbus_channel *channel, const uuid_le *type_gui
        int i;
        bool perf_chn = false;
        u32 max_cpus = num_online_cpus();
+       struct vmbus_channel *primary = channel->primary_channel, *prev;
+       unsigned long flags;
 
        for (i = IDE; i < MAX_PERF_CHN; i++) {
                if (!memcmp(type_guid->b, hp_devs[i].guid,
@@ -407,7 +409,32 @@ static void init_vp_index(struct vmbus_channel *channel, const uuid_le *type_gui
                channel->target_vp = 0;
                return;
        }
-       cur_cpu = (++next_vp % max_cpus);
+
+       /*
+        * Primary channels are distributed evenly across all vcpus we have.
+        * When the host asks us to create subchannels it usually makes us
+        * num_cpus-1 offers and we are supposed to distribute the work evenly
+        * among the channel itself and all its subchannels. Make sure they are
+        * all assigned to different vcpus.
+        */
+       if (!primary)
+               cur_cpu = (++next_vp % max_cpus);
+       else {
+               /*
+                * Let's assign the first subchannel of a channel to the
+                * primary->target_cpu+1 and all the subsequent channels to
+                * the prev->target_cpu+1.
+                */
+               spin_lock_irqsave(&primary->lock, flags);
+               if (primary->num_sc == 1)
+                       cur_cpu = (primary->target_cpu + 1) % max_cpus;
+               else {
+                       prev = list_prev_entry(channel, sc_list);
+                       cur_cpu = (prev->target_cpu + 1) % max_cpus;
+               }
+               spin_unlock_irqrestore(&primary->lock, flags);
+       }
+
        channel->target_cpu = cur_cpu;
        channel->target_vp = hv_context.vp_index[cur_cpu];
 }