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path: root/drivers/hv/ring_buffer.c
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Diffstat (limited to 'drivers/hv/ring_buffer.c')
-rw-r--r--drivers/hv/ring_buffer.c130
1 files changed, 113 insertions, 17 deletions
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 7233c88f01b8..cafa72ffdc30 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -29,6 +29,105 @@
#include "hyperv_vmbus.h"
+void hv_begin_read(struct hv_ring_buffer_info *rbi)
+{
+ rbi->ring_buffer->interrupt_mask = 1;
+ smp_mb();
+}
+
+u32 hv_end_read(struct hv_ring_buffer_info *rbi)
+{
+ u32 read;
+ u32 write;
+
+ rbi->ring_buffer->interrupt_mask = 0;
+ smp_mb();
+
+ /*
+ * Now check to see if the ring buffer is still empty.
+ * If it is not, we raced and we need to process new
+ * incoming messages.
+ */
+ hv_get_ringbuffer_availbytes(rbi, &read, &write);
+
+ return read;
+}
+
+/*
+ * When we write to the ring buffer, check if the host needs to
+ * be signaled. Here is the details of this protocol:
+ *
+ * 1. The host guarantees that while it is draining the
+ * ring buffer, it will set the interrupt_mask to
+ * indicate it does not need to be interrupted when
+ * new data is placed.
+ *
+ * 2. The host guarantees that it will completely drain
+ * the ring buffer before exiting the read loop. Further,
+ * once the ring buffer is empty, it will clear the
+ * interrupt_mask and re-check to see if new data has
+ * arrived.
+ */
+
+static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
+{
+ if (rbi->ring_buffer->interrupt_mask)
+ return false;
+
+ /*
+ * This is the only case we need to signal when the
+ * ring transitions from being empty to non-empty.
+ */
+ if (old_write == rbi->ring_buffer->read_index)
+ return true;
+
+ return false;
+}
+
+/*
+ * To optimize the flow management on the send-side,
+ * when the sender is blocked because of lack of
+ * sufficient space in the ring buffer, potential the
+ * consumer of the ring buffer can signal the producer.
+ * This is controlled by the following parameters:
+ *
+ * 1. pending_send_sz: This is the size in bytes that the
+ * producer is trying to send.
+ * 2. The feature bit feat_pending_send_sz set to indicate if
+ * the consumer of the ring will signal when the ring
+ * state transitions from being full to a state where
+ * there is room for the producer to send the pending packet.
+ */
+
+static bool hv_need_to_signal_on_read(u32 old_rd,
+ struct hv_ring_buffer_info *rbi)
+{
+ u32 prev_write_sz;
+ u32 cur_write_sz;
+ u32 r_size;
+ u32 write_loc = rbi->ring_buffer->write_index;
+ u32 read_loc = rbi->ring_buffer->read_index;
+ u32 pending_sz = rbi->ring_buffer->pending_send_sz;
+
+ /*
+ * If the other end is not blocked on write don't bother.
+ */
+ if (pending_sz == 0)
+ return false;
+
+ r_size = rbi->ring_datasize;
+ cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
+ read_loc - write_loc;
+
+ prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
+ old_rd - write_loc;
+
+
+ if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
+ return true;
+
+ return false;
+}
/*
* hv_get_next_write_location()
@@ -239,19 +338,6 @@ void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
}
}
-
-/*
- *
- * hv_get_ringbuffer_interrupt_mask()
- *
- * Get the interrupt mask for the specified ring buffer
- *
- */
-u32 hv_get_ringbuffer_interrupt_mask(struct hv_ring_buffer_info *rbi)
-{
- return rbi->ring_buffer->interrupt_mask;
-}
-
/*
*
* hv_ringbuffer_init()
@@ -298,7 +384,7 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
*
*/
int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
- struct scatterlist *sglist, u32 sgcount)
+ struct scatterlist *sglist, u32 sgcount, bool *signal)
{
int i = 0;
u32 bytes_avail_towrite;
@@ -307,6 +393,7 @@ int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
struct scatterlist *sg;
u32 next_write_location;
+ u32 old_write;
u64 prev_indices = 0;
unsigned long flags;
@@ -335,6 +422,8 @@ int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
/* Write to the ring buffer */
next_write_location = hv_get_next_write_location(outring_info);
+ old_write = next_write_location;
+
for_each_sg(sglist, sg, sgcount, i)
{
next_write_location = hv_copyto_ringbuffer(outring_info,
@@ -351,14 +440,16 @@ int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
&prev_indices,
sizeof(u64));
- /* Make sure we flush all writes before updating the writeIndex */
- smp_wmb();
+ /* Issue a full memory barrier before updating the write index */
+ smp_mb();
/* Now, update the write location */
hv_set_next_write_location(outring_info, next_write_location);
spin_unlock_irqrestore(&outring_info->ring_lock, flags);
+
+ *signal = hv_need_to_signal(old_write, outring_info);
return 0;
}
@@ -414,13 +505,14 @@ int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
*
*/
int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
- u32 buflen, u32 offset)
+ u32 buflen, u32 offset, bool *signal)
{
u32 bytes_avail_towrite;
u32 bytes_avail_toread;
u32 next_read_location = 0;
u64 prev_indices = 0;
unsigned long flags;
+ u32 old_read;
if (buflen <= 0)
return -EINVAL;
@@ -431,6 +523,8 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
&bytes_avail_toread,
&bytes_avail_towrite);
+ old_read = bytes_avail_toread;
+
/* Make sure there is something to read */
if (bytes_avail_toread < buflen) {
spin_unlock_irqrestore(&inring_info->ring_lock, flags);
@@ -461,5 +555,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
spin_unlock_irqrestore(&inring_info->ring_lock, flags);
+ *signal = hv_need_to_signal_on_read(old_read, inring_info);
+
return 0;
}