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Diffstat (limited to 'drivers/hv/connection.c')
-rw-r--r--drivers/hv/connection.c65
1 files changed, 34 insertions, 31 deletions
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index a8366fec1458..fce27fb141cc 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -296,44 +296,47 @@ struct vmbus_channel *relid2channel(u32 relid)
/*
* vmbus_on_event - Process a channel event notification
+ *
+ * For batched channels (default) 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.
+ * If this tasklet has been running for a long time
+ * then reschedule ourselves.
*/
void vmbus_on_event(unsigned long data)
{
struct vmbus_channel *channel = (void *) data;
- void (*callback_fn)(void *);
+ unsigned long time_limit = jiffies + 2;
- /*
- * A channel once created is persistent even when there
- * is no driver handling the device. An unloading driver
- * sets the onchannel_callback to NULL on the same CPU
- * as where this interrupt is handled (in an interrupt context).
- * Thus, checking and invoking the driver specific callback takes
- * care of orderly unloading of the driver.
- */
- callback_fn = READ_ONCE(channel->onchannel_callback);
- if (unlikely(callback_fn == NULL))
- return;
-
- (*callback_fn)(channel->channel_callback_context);
-
- if (channel->callback_mode == HV_CALL_BATCHED) {
- /*
- * 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 {
+ void (*callback_fn)(void *);
+
+ /* A channel once created is persistent even when
+ * there is no driver handling the device. An
+ * unloading driver sets the onchannel_callback to NULL.
*/
- if (hv_end_read(&channel->inbound) != 0) {
- hv_begin_read(&channel->inbound);
+ callback_fn = READ_ONCE(channel->onchannel_callback);
+ if (unlikely(callback_fn == NULL))
+ return;
- tasklet_schedule(&channel->callback_event);
- }
- }
+ (*callback_fn)(channel->channel_callback_context);
+
+ if (channel->callback_mode != HV_CALL_BATCHED)
+ return;
+
+ if (likely(hv_end_read(&channel->inbound) == 0))
+ return;
+
+ hv_begin_read(&channel->inbound);
+ } while (likely(time_before(jiffies, time_limit)));
+
+ /* The time limit (2 jiffies) has been reached */
+ tasklet_schedule(&channel->callback_event);
}
/*