Patchwork [v2,01/17] block: stop relying on io_flush() in bdrv_drain_all()

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Submitter Stefan Hajnoczi
Date April 17, 2013, 1:07 p.m.
Message ID <1366204073-8468-2-git-send-email-stefanha@redhat.com>
Download mbox | patch
Permalink /patch/237215/
State New
Headers show

Comments

Stefan Hajnoczi - April 17, 2013, 1:07 p.m.
If a block driver has no file descriptors to monitor but there are still
active requests, it can return 1 from .io_flush().  This is used to spin
during synchronous I/O.

Stop relying on .io_flush() and instead check
QLIST_EMPTY(&bs->tracked_requests) to decide whether there are active
requests.

This is the first step in removing .io_flush() so that event loops no
longer need to have the concept of synchronous I/O.  Eventually we may
be able to kill synchronous I/O completely by running everything in a
coroutine, but that is future work.

Note this patch moves bs->throttled_reqs initialization to bdrv_new() so
that bdrv_requests_pending(bs) can safely access it.  In practice bs is
g_malloc0() so the memory is already zeroed but it's safer to initialize
the queue properly.

In bdrv_delete() make sure to call bdrv_make_anon() *after* bdrv_close()
so that the device is still seen by bdrv_drain_all() when iterating
bdrv_states.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block.c | 47 ++++++++++++++++++++++++++++++++++-------------
 1 file changed, 34 insertions(+), 13 deletions(-)

Patch

diff --git a/block.c b/block.c
index 4ad663d..db08af5 100644
--- a/block.c
+++ b/block.c
@@ -151,7 +151,6 @@  static void bdrv_block_timer(void *opaque)
 
 void bdrv_io_limits_enable(BlockDriverState *bs)
 {
-    qemu_co_queue_init(&bs->throttled_reqs);
     bs->block_timer = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs);
     bs->io_limits_enabled = true;
 }
@@ -308,6 +307,7 @@  BlockDriverState *bdrv_new(const char *device_name)
     }
     bdrv_iostatus_disable(bs);
     notifier_list_init(&bs->close_notifiers);
+    qemu_co_queue_init(&bs->throttled_reqs);
 
     return bs;
 }
@@ -1360,6 +1360,35 @@  void bdrv_close_all(void)
     }
 }
 
+/* Check if any requests are in-flight (including throttled requests) */
+static bool bdrv_requests_pending(BlockDriverState *bs)
+{
+    if (!QLIST_EMPTY(&bs->tracked_requests)) {
+        return true;
+    }
+    if (!qemu_co_queue_empty(&bs->throttled_reqs)) {
+        return true;
+    }
+    if (bs->file && bdrv_requests_pending(bs->file)) {
+        return true;
+    }
+    if (bs->backing_hd && bdrv_requests_pending(bs->backing_hd)) {
+        return true;
+    }
+    return false;
+}
+
+static bool bdrv_requests_pending_all(void)
+{
+    BlockDriverState *bs;
+    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+        if (bdrv_requests_pending(bs)) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /*
  * Wait for pending requests to complete across all BlockDriverStates
  *
@@ -1375,26 +1404,18 @@  void bdrv_close_all(void)
 void bdrv_drain_all(void)
 {
     BlockDriverState *bs;
-    bool busy;
-
-    do {
-        busy = qemu_aio_wait();
 
+    while (bdrv_requests_pending_all()) {
         /* FIXME: We do not have timer support here, so this is effectively
          * a busy wait.
          */
         QTAILQ_FOREACH(bs, &bdrv_states, list) {
             if (!qemu_co_queue_empty(&bs->throttled_reqs)) {
                 qemu_co_queue_restart_all(&bs->throttled_reqs);
-                busy = true;
             }
         }
-    } while (busy);
 
-    /* If requests are still pending there is a bug somewhere */
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
-        assert(QLIST_EMPTY(&bs->tracked_requests));
-        assert(qemu_co_queue_empty(&bs->throttled_reqs));
+        qemu_aio_wait();
     }
 }
 
@@ -1539,11 +1560,11 @@  void bdrv_delete(BlockDriverState *bs)
     assert(!bs->job);
     assert(!bs->in_use);
 
+    bdrv_close(bs);
+
     /* remove from list, if necessary */
     bdrv_make_anon(bs);
 
-    bdrv_close(bs);
-
     assert(bs != bs_snapshots);
     g_free(bs);
 }