chardev: remove write polling

In an effort to reduce the wakeups per second, get rid of the
"write_to_dev" timer when the implementation supports
SPICE_CHAR_DEVICE_NOTIFY_WRITABLE.

When this flag is set, the frontend instance is responsible for calling
spice_char_device_wakeup() when the device is ready to perform IO.

Related to:
https://bugzilla.redhat.com/show_bug.cgi?id=912763

2 files changed, 34 insertions, 11 deletions

diff --git a/server/char_device.c b/server/char_device.c
index 6d2339e8..c6dc45b9 100644
--- a/server/char_device.c
+++ b/server/char_device.c
@@ -438,7 +438,10 @@ static int spice_char_device_write_to_device(SpiceCharDeviceState *dev)
     }
 
     spice_char_device_state_ref(dev);
-    core->timer_cancel(dev->write_to_dev_timer);
+
+    if (dev->write_to_dev_timer) {
+        core->timer_cancel(dev->write_to_dev_timer);
+    }
 
     sif = SPICE_CONTAINEROF(dev->sin->base.sif, SpiceCharDeviceInterface, base);
     while (dev->running) {
@@ -473,8 +476,10 @@ static int spice_char_device_write_to_device(SpiceCharDeviceState *dev)
     /* retry writing as long as the write queue is not empty */
     if (dev->running) {
         if (dev->cur_write_buf) {
-            core->timer_start(dev->write_to_dev_timer,
-                              CHAR_DEVICE_WRITE_TO_TIMEOUT);
+            if (dev->write_to_dev_timer) {
+                core->timer_start(dev->write_to_dev_timer,
+                                  CHAR_DEVICE_WRITE_TO_TIMEOUT);
+            }
         } else {
             spice_assert(ring_is_empty(&dev->write_queue));
         }
@@ -488,7 +493,9 @@ static void spice_char_dev_write_retry(void *opaque)
 {
     SpiceCharDeviceState *dev = opaque;
 
-    core->timer_cancel(dev->write_to_dev_timer);
+    if (dev->write_to_dev_timer) {
+        core->timer_cancel(dev->write_to_dev_timer);
+    }
     spice_char_device_write_to_device(dev);
 }
 
@@ -635,6 +642,7 @@ SpiceCharDeviceState *spice_char_device_state_create(SpiceCharDeviceInstance *si
                                                      void *opaque)
 {
     SpiceCharDeviceState *char_dev;
+    SpiceCharDeviceInterface *sif;
 
     spice_assert(sin);
     spice_assert(cbs->read_one_msg_from_device && cbs->ref_msg_to_client &&
@@ -652,10 +660,15 @@ SpiceCharDeviceState *spice_char_device_state_create(SpiceCharDeviceInstance *si
     ring_init(&char_dev->write_bufs_pool);
     ring_init(&char_dev->clients);
 
-    char_dev->write_to_dev_timer = core->timer_add(spice_char_dev_write_retry, char_dev);
-    if (!char_dev->write_to_dev_timer) {
-        spice_error("failed creating char dev write timer");
+    sif = SPICE_CONTAINEROF(char_dev->sin->base.sif, SpiceCharDeviceInterface, base);
+    if (sif->base.minor_version <= 2 ||
+        !(sif->flags & SPICE_CHAR_DEVICE_NOTIFY_WRITABLE)) {
+        char_dev->write_to_dev_timer = core->timer_add(spice_char_dev_write_retry, char_dev);
+        if (!char_dev->write_to_dev_timer) {
+            spice_error("failed creating char dev write timer");
+        }
     }
+
     char_dev->refs = 1;
     sin->st = char_dev;
     spice_debug("sin %p dev_state %p", sin, char_dev);
@@ -697,7 +710,9 @@ static void spice_char_device_state_unref(SpiceCharDeviceState *char_dev)
 void spice_char_device_state_destroy(SpiceCharDeviceState *char_dev)
 {
     reds_on_char_device_state_destroy(char_dev);
-    core->timer_remove(char_dev->write_to_dev_timer);
+    if (char_dev->write_to_dev_timer) {
+        core->timer_remove(char_dev->write_to_dev_timer);
+    }
     write_buffers_queue_free(&char_dev->write_queue);
     write_buffers_queue_free(&char_dev->write_bufs_pool);
     if (char_dev->cur_write_buf) {
@@ -805,7 +820,9 @@ void spice_char_device_stop(SpiceCharDeviceState *dev)
     spice_debug("dev_state %p", dev);
     dev->running = FALSE;
     dev->active = FALSE;
-    core->timer_cancel(dev->write_to_dev_timer);
+    if (dev->write_to_dev_timer) {
+        core->timer_cancel(dev->write_to_dev_timer);
+    }
 }
 
 void spice_char_device_reset(SpiceCharDeviceState *dev)
@@ -842,6 +859,7 @@ void spice_char_device_reset(SpiceCharDeviceState *dev)
 
 void spice_char_device_wakeup(SpiceCharDeviceState *dev)
 {
+    spice_char_device_write_to_device(dev);
     spice_char_device_read_from_device(dev);
 }
 
diff --git a/server/spice.h b/server/spice.h
index 58700d14..bd5bba89 100644
--- a/server/spice.h
+++ b/server/spice.h
@@ -24,7 +24,7 @@
 #include <spice/vd_agent.h>
 #include <spice/macros.h>
 
-#define SPICE_SERVER_VERSION 0x000c05 /* release 0.12.5 */
+#define SPICE_SERVER_VERSION 0x000c06 /* release 0.12.6 */
 
 #ifdef SPICE_SERVER_INTERNAL
 #undef SPICE_GNUC_DEPRECATED
@@ -402,11 +402,15 @@ void     spice_server_set_record_rate(SpiceRecordInstance *sin, uint32_t frequen
 
 #define SPICE_INTERFACE_CHAR_DEVICE "char_device"
 #define SPICE_INTERFACE_CHAR_DEVICE_MAJOR 1
-#define SPICE_INTERFACE_CHAR_DEVICE_MINOR 2
+#define SPICE_INTERFACE_CHAR_DEVICE_MINOR 3
 typedef struct SpiceCharDeviceInterface SpiceCharDeviceInterface;
 typedef struct SpiceCharDeviceInstance SpiceCharDeviceInstance;
 typedef struct SpiceCharDeviceState SpiceCharDeviceState;
 
+typedef enum {
+    SPICE_CHAR_DEVICE_NOTIFY_WRITABLE = 1 << 0,
+} spice_char_device_flags;
+
 struct SpiceCharDeviceInterface {
     SpiceBaseInterface base;
 
@@ -414,6 +418,7 @@ struct SpiceCharDeviceInterface {
     int (*write)(SpiceCharDeviceInstance *sin, const uint8_t *buf, int len);
     int (*read)(SpiceCharDeviceInstance *sin, uint8_t *buf, int len);
     void (*event)(SpiceCharDeviceInstance *sin, uint8_t event);
+    spice_char_device_flags flags;
 };
 
 struct SpiceCharDeviceInstance {