1 files changed, 30 insertions, 2 deletions

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 42fe43fb0c80..183efde54269 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -128,6 +128,7 @@ struct hv_ring_buffer_info {
         u32 ring_data_startoffset;
         u32 priv_write_index;
         u32 priv_read_index;
+        u32 cached_read_index;
 };
 
 /*
@@ -180,6 +181,19 @@ static inline u32 hv_get_bytes_to_write(struct hv_ring_buffer_info *rbi)
         return write;
 }
 
+static inline u32 hv_get_cached_bytes_to_write(
+        const struct hv_ring_buffer_info *rbi)
+{
+        u32 read_loc, write_loc, dsize, write;
+
+        dsize = rbi->ring_datasize;
+        read_loc = rbi->cached_read_index;
+        write_loc = rbi->ring_buffer->write_index;
+
+        write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
+                read_loc - write_loc;
+        return write;
+}
 /*
  * VMBUS version is 32 bit entity broken up into
  * two 16 bit quantities: major_number. minor_number.
@@ -1488,7 +1502,7 @@ hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
 
 static inline  void hv_signal_on_read(struct vmbus_channel *channel)
 {
-        u32 cur_write_sz;
+        u32 cur_write_sz, cached_write_sz;
         u32 pending_sz;
         struct hv_ring_buffer_info *rbi = &channel->inbound;
 
@@ -1512,12 +1526,24 @@ static inline  void hv_signal_on_read(struct vmbus_channel *channel)
 
         cur_write_sz = hv_get_bytes_to_write(rbi);
 
-        if (cur_write_sz >= pending_sz)
+        if (cur_write_sz < pending_sz)
+                return;
+
+        cached_write_sz = hv_get_cached_bytes_to_write(rbi);
+        if (cached_write_sz < pending_sz)
                 vmbus_setevent(channel);
 
         return;
 }
 
+static inline void
+init_cached_read_index(struct vmbus_channel *channel)
+{
+        struct hv_ring_buffer_info *rbi = &channel->inbound;
+
+        rbi->cached_read_index = rbi->ring_buffer->read_index;
+}
+
 /*
  * An API to support in-place processing of incoming VMBUS packets.
  */
@@ -1569,6 +1595,8 @@ static inline void put_pkt_raw(struct vmbus_channel *channel,
  * This call commits the read index and potentially signals the host.
  * Here is the pattern for using the "in-place" consumption APIs:
  *
+ * init_cached_read_index();
+ *
  * while (get_next_pkt_raw() {
  *      process the packet "in-place";
  *      put_pkt_raw();