vhost: support interrupt mode

vhost currently supports only polling mode. This patch is to add
interrupt mode. When the interface is configured for interrupt
mode, our input node does not get called unless there is a packet
in the vring.

If a particular CPU has one interface configured for polling mode
and another in interrupt, the input node is set to polling for
that CPU.

This diffs also includes two crashes in vlib's dispatch_node. One is
included in https://gerrit.fd.io/r/#/c/5516. The other crash is in
the ASSERT. The ASSERT can become true when the caller of
dispatch_node is in a loop. The first call converted the node
to polling. The second call thereafter will hit the ASSERT.

Change-Id: If17b6d48b20d7d8605c6a161459828637173cd32
Signed-off-by: Steven <sluong@cisco.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/vnet/devices/virtio/vhost-user.h b/src/vnet/devices/virtio/vhost-user.h
index 6b928f05e28..67f18b8ed8e 100644
--- a/src/vnet/devices/virtio/vhost-user.h
+++ b/src/vnet/devices/virtio/vhost-user.h
@@ -216,6 +216,8 @@ typedef struct
 #define VHOST_USER_INTERRUPT_MODE 1
 #define VHOST_USER_ADAPTIVE_MODE  2
 
+#define VHOST_USER_EVENT_START_TIMER 1
+
 typedef struct
 {
   CLIB_CACHE_LINE_ALIGN_MARK (cacheline0);
@@ -298,6 +300,12 @@ typedef struct
   /* This is here so it doesn't end-up
    * using stack or registers. */
   vhost_trace_t *current_trace;
+
+  /* bitmap of pending rx interfaces */
+  uword *pending_input_bitmap;
+
+  /* The operation mode computed per cpu based on interface setting */
+  u8 operation_mode;
 } vhost_cpu_t;
 
 typedef struct
@@ -320,6 +328,9 @@ typedef struct
 
   /** Pseudo random iterator */
   u32 random;
+
+  /* Node is in interrupt mode */
+  u8 interrupt_mode;
 } vhost_user_main_t;
 
 typedef struct