[Qemu-devel] [PATCH] virtio-serial-bus: use bh for unthrottling

[Alon Levy]

Instead of calling flush_queued_data when unthrottling, schedule
a bh. That way we can return immediately to the caller, and the
flush uses the same call path as a have_data for callbackee.

migration: since version 2 of the migration protocol we unthrottle
if there is data. So we don't need to add anything special here, just
the unthrottling mechanism changed, from directl function call to bh.
---
 hw/virtio-serial-bus.c |   11 +++++++++--
 hw/virtio-serial.h     |    5 +++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index a82fbe9..e8a892d 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -285,6 +285,13 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort *port)
     return 0;
 }
 
+static void bh_virtio_serial_flush_queued_data(void *opaque)
+{
+    VirtIOSerialPort *port = opaque;
+
+    flush_queued_data(port);
+}
+
 void virtio_serial_throttle_port(VirtIOSerialPort *port, bool throttle)
 {
     if (!port) {
@@ -295,8 +302,7 @@ void virtio_serial_throttle_port(VirtIOSerialPort *port, 
bool throttle)
     if (throttle) {
         return;
     }
-
-    flush_queued_data(port);
+    qemu_bh_schedule(port->bh);
 }
 
 /* Guest wants to notify us of some event */
@@ -721,6 +727,7 @@ static int virtser_port_qdev_init(DeviceState *qdev, 
DeviceInfo *base)
     bool plugging_port0;
 
     port->vser = bus->vser;
+    port->bh = qemu_bh_new(bh_virtio_serial_flush_queued_data, port);
 
     /*
      * Is the first console port we're seeing? If so, put it up at
diff --git a/hw/virtio-serial.h b/hw/virtio-serial.h
index 5eb948e..0fa03d1 100644
--- a/hw/virtio-serial.h
+++ b/hw/virtio-serial.h
@@ -119,6 +119,11 @@ struct VirtIOSerialPort {
     uint32_t iov_idx;
     uint64_t iov_offset;
 
+    /*
+     * When unthrottling we use a buttomhalf to call flush_queued_data.
+     */
+    QEMUBH *bh;
+
     /* Identify if this is a port that binds with hvc in the guest */
     uint8_t is_console;
 
-- 
1.7.4.1