rbd: record aggregate image transfer count

Compute the total number of bytes transferred for an image
request--the sum across each of the request's object requests.
To avoid contention do it only when all object requests are
complete, in rbd_img_request_complete().

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 69eab66b6c67..e8374aec93da 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -214,6 +214,7 @@ struct rbd_img_request {
         spinlock_t              completion_lock;/* protects next_completion */
         u32                     next_completion;
         rbd_img_callback_t      callback;
+        u64                     xferred;/* aggregate bytes transferred */
         int                     result; /* first nonzero obj_request result */
 
         u32                     obj_request_count;
@@ -1148,7 +1149,24 @@ static int rbd_obj_request_submit(struct ceph_osd_client *osdc,
 
 static void rbd_img_request_complete(struct rbd_img_request *img_request)
 {
+
         dout("%s: img %p\n", __func__, img_request);
+
+        /*
+         * If no error occurred, compute the aggregate transfer
+         * count for the image request.  We could instead use
+         * atomic64_cmpxchg() to update it as each object request
+         * completes; not clear which way is better off hand.
+         */
+        if (!img_request->result) {
+                struct rbd_obj_request *obj_request;
+                u64 xferred = 0;
+
+                for_each_obj_request(img_request, obj_request)
+                        xferred += obj_request->xferred;
+                img_request->xferred = xferred;
+        }
+
         if (img_request->callback)
                 img_request->callback(img_request);
         else