[Qemu-devel] [PATCH v2 06/16] block: add BDS field to count in-flight requests

[Paolo Bonzini]

Unlike tracked_requests, this field also counts throttled requests,
and remains non-zero if an AIO operation needs a BH to be "really"
completed.

With this change, it is no longer necessary to have a dummy
BdrvTrackedRequest for requests that are never serialising, and
it is no longer necessary to poll the AioContext once after
bdrv_requests_pending(bs) returns false.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 block/io.c                | 71 +++++++++++++++++++++++++++++++----------------
 block/mirror.c            |  2 ++
 include/block/block_int.h |  8 ++++--
 3 files changed, 54 insertions(+), 27 deletions(-)

diff --git a/block/io.c b/block/io.c
index d8d50b7..a9a23a6 100644
--- a/block/io.c
+++ b/block/io.c
@@ -224,13 +224,7 @@ bool bdrv_requests_pending(BlockDriverState *bs)
 {
     BdrvChild *child;
 
-    if (!QLIST_EMPTY(&bs->tracked_requests)) {
-        return true;
-    }
-    if (!qemu_co_queue_empty(&bs->throttled_reqs[0])) {
-        return true;
-    }
-    if (!qemu_co_queue_empty(&bs->throttled_reqs[1])) {
+    if (atomic_read(&bs->in_flight)) {
         return true;
     }
 
@@ -268,15 +262,12 @@ static void bdrv_drain_recurse(BlockDriverState *bs)
  */
 void bdrv_drain(BlockDriverState *bs)
 {
-    bool busy = true;
-
     bdrv_no_throttling_begin(bs);
     bdrv_io_unplugged_begin(bs);
     bdrv_drain_recurse(bs);
-    while (busy) {
+    while (bdrv_requests_pending(bs)) {
         /* Keep iterating */
-         busy = bdrv_requests_pending(bs);
-         busy |= aio_poll(bdrv_get_aio_context(bs), busy);
+         aio_poll(bdrv_get_aio_context(bs), true);
     }
     bdrv_io_unplugged_end(bs);
     bdrv_no_throttling_end(bs);
@@ -291,7 +282,7 @@ void bdrv_drain(BlockDriverState *bs)
 void bdrv_drain_all(void)
 {
     /* Always run first iteration so any pending completion BHs run */
-    bool busy = true;
+    bool waited = true;
     BlockDriverState *bs = NULL;
     GSList *aio_ctxs = NULL, *ctx;
 
@@ -318,8 +309,8 @@ void bdrv_drain_all(void)
      * request completion.  Therefore we must keep looping until there was no
      * more activity rather than simply draining each device independently.
      */
-    while (busy) {
-        busy = false;
+    while (waited) {
+        waited = false;
 
         for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) {
             AioContext *aio_context = ctx->data;
@@ -329,12 +320,11 @@ void bdrv_drain_all(void)
             while ((bs = bdrv_next(bs))) {
                 if (aio_context == bdrv_get_aio_context(bs)) {
                     if (bdrv_requests_pending(bs)) {
-                        busy = true;
-                        aio_poll(aio_context, busy);
+                        aio_poll(aio_context, true);
+                        waited = true;
                     }
                 }
             }
-            busy |= aio_poll(aio_context, false);
             aio_context_release(aio_context);
         }
     }
@@ -457,6 +447,16 @@ static bool tracked_request_overlaps(BdrvTrackedRequest 
*req,
     return true;
 }
 
+void bdrv_inc_in_flight(BlockDriverState *bs)
+{
+    atomic_inc(&bs->in_flight);
+}
+
+void bdrv_dec_in_flight(BlockDriverState *bs)
+{
+    atomic_dec(&bs->in_flight);
+}
+
 static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
 {
     BlockDriverState *bs = self->bs;
@@ -963,6 +963,8 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState 
*bs,
         return ret;
     }
 
+    bdrv_inc_in_flight(bs);
+
     /* Don't do copy-on-read if we read data before write operation */
     if (bs->copy_on_read && !(flags & BDRV_REQ_NO_SERIALISING)) {
         flags |= BDRV_REQ_COPY_ON_READ;
@@ -1003,6 +1005,7 @@ static int coroutine_fn 
bdrv_co_do_preadv(BlockDriverState *bs,
                               use_local_qiov ? &local_qiov : qiov,
                               flags);
     tracked_request_end(&req);
+    bdrv_dec_in_flight(bs);
 
     if (use_local_qiov) {
         qemu_iovec_destroy(&local_qiov);
@@ -1310,6 +1313,8 @@ static int coroutine_fn 
bdrv_co_do_pwritev(BlockDriverState *bs,
         return ret;
     }
 
+    bdrv_inc_in_flight(bs);
+
     /* throttling disk I/O */
     if (bs->throttle_state) {
         throttle_group_co_io_limits_intercept(bs, bytes, true);
@@ -1408,6 +1413,7 @@ fail:
     qemu_vfree(tail_buf);
 out:
     tracked_request_end(&req);
+    bdrv_dec_in_flight(bs);
     return ret;
 }
 
@@ -2065,6 +2071,7 @@ static const AIOCBInfo bdrv_em_aiocb_info = {
 static void bdrv_aio_bh_cb(void *opaque)
 {
     BlockAIOCBSync *acb = opaque;
+    BlockDriverState *bs = acb->common.bs;
 
     if (!acb->is_write && acb->ret >= 0) {
         qemu_iovec_from_buf(acb->qiov, 0, acb->bounce, acb->qiov->size);
@@ -2072,6 +2079,7 @@ static void bdrv_aio_bh_cb(void *opaque)
     qemu_vfree(acb->bounce);
     acb->common.cb(acb->common.opaque, acb->ret);
     qemu_bh_delete(acb->bh);
+    bdrv_dec_in_flight(bs);
     acb->bh = NULL;
     qemu_aio_unref(acb);
 }
@@ -2087,6 +2095,7 @@ static BlockAIOCB *bdrv_aio_rw_vector(BlockDriverState 
*bs,
 {
     BlockAIOCBSync *acb;
 
+    bdrv_inc_in_flight(bs);
     acb = qemu_aio_get(&bdrv_em_aiocb_info, bs, cb, opaque);
     acb->is_write = is_write;
     acb->qiov = qiov;
@@ -2139,6 +2148,7 @@ static void bdrv_co_complete(BlockAIOCBCoroutine *acb)
 {
     if (!acb->need_bh) {
         acb->common.cb(acb->common.opaque, acb->req.error);
+        bdrv_dec_in_flight(acb->common.bs);
         qemu_aio_unref(acb);
     }
 }
@@ -2192,6 +2202,9 @@ static BlockAIOCB *bdrv_co_aio_rw_vector(BlockDriverState 
*bs,
     Coroutine *co;
     BlockAIOCBCoroutine *acb;
 
+    /* Matched by bdrv_co_complete's bdrv_dec_in_flight.  */
+    bdrv_inc_in_flight(bs);
+
     acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
     acb->need_bh = true;
     acb->req.error = -EINPROGRESS;
@@ -2225,6 +2238,9 @@ BlockAIOCB *bdrv_aio_flush(BlockDriverState *bs,
     Coroutine *co;
     BlockAIOCBCoroutine *acb;
 
+    /* Matched by bdrv_co_complete's bdrv_dec_in_flight.  */
+    bdrv_inc_in_flight(bs);
+
     acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
     acb->need_bh = true;
     acb->req.error = -EINPROGRESS;
@@ -2254,6 +2270,9 @@ BlockAIOCB *bdrv_aio_discard(BlockDriverState *bs,
 
     trace_bdrv_aio_discard(bs, sector_num, nb_sectors, opaque);
 
+    /* Matched by bdrv_co_complete's bdrv_dec_in_flight.  */
+    bdrv_inc_in_flight(bs);
+
     acb = qemu_aio_get(&bdrv_em_co_aiocb_info, bs, cb, opaque);
     acb->need_bh = true;
     acb->req.error = -EINPROGRESS;
@@ -2361,14 +2380,14 @@ static void coroutine_fn bdrv_flush_co_entry(void 
*opaque)
 int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
 {
     int ret;
-    BdrvTrackedRequest req;
 
     if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) ||
         bdrv_is_sg(bs)) {
         return 0;
     }
 
-    tracked_request_begin(&req, bs, 0, 0, BDRV_TRACKED_FLUSH);
+    bdrv_inc_in_flight(bs);
+
     /* Write back cached data to the OS even with cache=unsafe */
     BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS);
     if (bs->drv->bdrv_co_flush_to_os) {
@@ -2423,7 +2442,7 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
 flush_parent:
     ret = bs->file ? bdrv_co_flush(bs->file->bs) : 0;
 out:
-    tracked_request_end(&req);
+    bdrv_dec_in_flight(bs);
     return ret;
 }
 
@@ -2491,6 +2510,7 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, 
int64_t sector_num,
         return 0;
     }
 
+    bdrv_inc_in_flight(bs);
     tracked_request_begin(&req, bs, sector_num, nb_sectors,
                           BDRV_TRACKED_DISCARD);
     bdrv_set_dirty(bs, sector_num, nb_sectors);
@@ -2543,6 +2563,7 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, 
int64_t sector_num,
     ret = 0;
 out:
     tracked_request_end(&req);
+    bdrv_dec_in_flight(bs);
     return ret;
 }
 
@@ -2588,13 +2609,12 @@ static void bdrv_ioctl_bh_cb(void *opaque)
 static int bdrv_co_do_ioctl(BlockDriverState *bs, int req, void *buf)
 {
     BlockDriver *drv = bs->drv;
-    BdrvTrackedRequest tracked_req;
     CoroutineIOCompletion co = {
         .coroutine = qemu_coroutine_self(),
     };
     BlockAIOCB *acb;
 
-    tracked_request_begin(&tracked_req, bs, 0, 0, BDRV_TRACKED_IOCTL);
+    bdrv_inc_in_flight(bs);
     if (!drv || !drv->bdrv_aio_ioctl) {
         co.ret = -ENOTSUP;
         goto out;
@@ -2610,7 +2630,7 @@ static int bdrv_co_do_ioctl(BlockDriverState *bs, int 
req, void *buf)
     }
     qemu_coroutine_yield();
 out:
-    tracked_request_end(&tracked_req);
+    bdrv_dec_in_flight(bs);
     return co.ret;
 }
 
@@ -2667,6 +2687,9 @@ BlockAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
                                             bs, cb, opaque);
     Coroutine *co;
 
+    /* Matched by bdrv_co_complete's bdrv_dec_in_flight.  */
+    bdrv_inc_in_flight(bs);
+
     acb->need_bh = true;
     acb->req.error = -EINPROGRESS;
     acb->req.req = req;
diff --git a/block/mirror.c b/block/mirror.c
index 2c7874d..1aecafd 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -95,6 +95,7 @@ static void mirror_bh_cb(void *opaque)
 
     qemu_bh_delete(op->co_enter_bh);
     g_free(op);
+    bdrv_dec_in_flight(s->common.bs);
     if (s->waiting_for_io) {
         qemu_coroutine_enter(s->common.co, NULL);
     }
@@ -135,6 +136,7 @@ static void mirror_iteration_done(MirrorOp *op, int ret)
      * If we call qemu_coroutine_enter here, there is the possibility
      * of a deadlock when the coroutine calls bdrv_drained_begin.
      */
+    bdrv_inc_in_flight(s->common.bs);
     op->co_enter_bh = aio_bh_new(bdrv_get_aio_context(s->target),
                                  mirror_bh_cb, op);
     qemu_bh_schedule(op->co_enter_bh);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 13136a3..b0311ac 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -63,8 +63,6 @@
 enum BdrvTrackedRequestType {
     BDRV_TRACKED_READ,
     BDRV_TRACKED_WRITE,
-    BDRV_TRACKED_FLUSH,
-    BDRV_TRACKED_IOCTL,
     BDRV_TRACKED_DISCARD,
 };
 
@@ -406,7 +404,8 @@ struct BlockDriverState {
     /* Callback before write request is processed */
     NotifierWithReturnList before_write_notifiers;
 
-    /* number of in-flight serialising requests */
+    /* number of in-flight requests; overall and serialising */
+    unsigned int in_flight;
     unsigned int serialising_in_flight;
 
     /* I/O throttling.
@@ -715,6 +714,9 @@ bool bdrv_requests_pending(BlockDriverState *bs);
 void bdrv_clear_dirty_bitmap(BdrvDirtyBitmap *bitmap, HBitmap **out);
 void bdrv_undo_clear_dirty_bitmap(BdrvDirtyBitmap *bitmap, HBitmap *in);
 
+void bdrv_inc_in_flight(BlockDriverState *bs);
+void bdrv_dec_in_flight(BlockDriverState *bs);
+
 void blockdev_close_all_bdrv_states(void);
 
 #endif /* BLOCK_INT_H */
-- 
1.8.3.1