diff options
Diffstat (limited to 'drivers/hv/ring_buffer.c')
| -rw-r--r-- | drivers/hv/ring_buffer.c | 42 |
1 files changed, 39 insertions, 3 deletions
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c index 00107928770..9bc55f0dcf4 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -53,6 +53,37 @@ u32 hv_end_read(struct hv_ring_buffer_info *rbi) 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; +} + /* * hv_get_next_write_location() @@ -322,7 +353,7 @@ 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; @@ -331,6 +362,7 @@ 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; @@ -359,6 +391,8 @@ 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, @@ -375,14 +409,16 @@ 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; } |