Drivers: hv: Optimize signaling in the read path

Now that we have the infratructure for correctly determining when we
should signal the host; optimize the signaling on the read side -
signaling the guest from the host.

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, 25 insertions, 3 deletions

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 650c9f0b6642..d1019a770ad7 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -212,6 +212,9 @@ static void process_chn_event(u32 relid)
 {
         struct vmbus_channel *channel;
         unsigned long flags;
+        void *arg;
+        bool read_state;
+        u32 bytes_to_read;
 
         /*
          * Find the channel based on this relid and invokes the
@@ -234,10 +237,29 @@ static void process_chn_event(u32 relid)
          */
 
         spin_lock_irqsave(&channel->inbound_lock, flags);
-        if (channel->onchannel_callback != NULL)
-                channel->onchannel_callback(channel->channel_callback_context);
-        else
+        if (channel->onchannel_callback != NULL) {
+                arg = channel->channel_callback_context;
+                read_state = channel->batched_reading;
+                /*
+                 * This callback reads the messages sent by the host.
+                 * We can optimize host to guest signaling by ensuring:
+                 * 1. While reading the channel, we disable interrupts from
+                 *    host.
+                 * 2. Ensure that we process all posted messages from the host
+                 *    before returning from this callback.
+                 * 3. Once we return, enable signaling from the host. Once this
+                 *    state is set we check to see if additional packets are
+                 *    available to read. In this case we repeat the process.
+                 */
+
+                do {
+                        hv_begin_read(&channel->inbound);
+                        channel->onchannel_callback(arg);
+                        bytes_to_read = hv_end_read(&channel->inbound);
+                } while (read_state && (bytes_to_read != 0));
+        } else {
                 pr_err("no channel callback for relid - %u\n", relid);
+        }
 
         spin_unlock_irqrestore(&channel->inbound_lock, flags);
 }