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Re: [PATCH 07/12] block/io.c: introduce bdrv_subtree_drained_{begin/end}


From: Paolo Bonzini
Subject: Re: [PATCH 07/12] block/io.c: introduce bdrv_subtree_drained_{begin/end}_unlocked
Date: Wed, 19 Jan 2022 10:52:54 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0

On 1/18/22 17:27, Emanuele Giuseppe Esposito wrote:
Same as the locked version, but use BDRV_POLL_UNLOCKED

... We are going to add drains to all graph modifications, and they are generally performed without the AioContext lock taken.

Paolo

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
  block/io.c               | 50 +++++++++++++++++++++++++++++-----------
  include/block/block-io.h |  2 ++
  2 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/block/io.c b/block/io.c
index 5123b7b713..9d5167f64a 100644
--- a/block/io.c
+++ b/block/io.c
@@ -244,6 +244,7 @@ typedef struct {
      bool begin;
      bool recursive;
      bool poll;
+    bool unlock;
      BdrvChild *parent;
      bool ignore_bds_parents;
      int *drained_end_counter;
@@ -334,7 +335,7 @@ static bool bdrv_drain_poll_top_level(BlockDriverState *bs, 
bool recursive,
static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
                                    BdrvChild *parent, bool ignore_bds_parents,
-                                  bool poll);
+                                  bool poll, bool unlock);
  static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
                                  BdrvChild *parent, bool ignore_bds_parents,
                                  int *drained_end_counter);
@@ -352,7 +353,8 @@ static void bdrv_co_drain_bh_cb(void *opaque)
          if (data->begin) {
              assert(!data->drained_end_counter);
              bdrv_do_drained_begin(bs, data->recursive, data->parent,
-                                  data->ignore_bds_parents, data->poll);
+                                  data->ignore_bds_parents, data->poll,
+                                  data->unlock);
          } else {
              assert(!data->poll);
              bdrv_do_drained_end(bs, data->recursive, data->parent,
@@ -374,6 +376,7 @@ static void coroutine_fn 
bdrv_co_yield_to_drain(BlockDriverState *bs,
                                                  BdrvChild *parent,
                                                  bool ignore_bds_parents,
                                                  bool poll,
+                                                bool unlock,
                                                  int *drained_end_counter)
  {
      BdrvCoDrainData data;
@@ -394,6 +397,7 @@ static void coroutine_fn 
bdrv_co_yield_to_drain(BlockDriverState *bs,
          .parent = parent,
          .ignore_bds_parents = ignore_bds_parents,
          .poll = poll,
+        .unlock = unlock,
          .drained_end_counter = drained_end_counter,
      };
@@ -441,13 +445,13 @@ static void bdrv_do_drained_begin_quiesce(BlockDriverState *bs, static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
                                    BdrvChild *parent, bool ignore_bds_parents,
-                                  bool poll)
+                                  bool poll, bool unlock)
  {
      BdrvChild *child, *next;
if (qemu_in_coroutine()) {
          bdrv_co_yield_to_drain(bs, true, recursive, parent, 
ignore_bds_parents,
-                               poll, NULL);
+                               poll, unlock, NULL);
          return;
      }
@@ -458,7 +462,7 @@ static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
          bs->recursive_quiesce_counter++;
          QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
              bdrv_do_drained_begin(child->bs, true, child, ignore_bds_parents,
-                                  false);
+                                  false, false);
          }
      }
@@ -473,23 +477,35 @@ static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
       */
      if (poll) {
          assert(!ignore_bds_parents);
-        BDRV_POLL_WHILE(bs, bdrv_drain_poll_top_level(bs, recursive, parent));
+        if (unlock) {
+            BDRV_POLL_WHILE_UNLOCKED(bs,
+                                     bdrv_drain_poll_top_level(bs, recursive,
+                                                               parent));
+        } else {
+            BDRV_POLL_WHILE(bs,
+                            bdrv_drain_poll_top_level(bs, recursive, parent));
+        }
      }
  }
void bdrv_drained_begin(BlockDriverState *bs)
  {
-    bdrv_do_drained_begin(bs, false, NULL, false, true);
+    bdrv_do_drained_begin(bs, false, NULL, false, true, false);
  }
void bdrv_subtree_drained_begin(BlockDriverState *bs)
  {
-    bdrv_do_drained_begin(bs, true, NULL, false, true);
+    bdrv_do_drained_begin(bs, true, NULL, false, true, false);
+}
+
+void bdrv_subtree_drained_begin_unlocked(BlockDriverState *bs)
+{
+    bdrv_do_drained_begin(bs, true, NULL, false, true, true);
  }
void bdrv_drained_begin_no_poll(BlockDriverState *bs)
  {
-    bdrv_do_drained_begin(bs, false, NULL, false, false);
+    bdrv_do_drained_begin(bs, false, NULL, false, false, false);
  }
/**
@@ -517,7 +533,7 @@ static void bdrv_do_drained_end(BlockDriverState *bs, bool 
recursive,
if (qemu_in_coroutine()) {
          bdrv_co_yield_to_drain(bs, false, recursive, parent, 
ignore_bds_parents,
-                               false, drained_end_counter);
+                               false, false, drained_end_counter);
          return;
      }
      assert(bs->quiesce_counter > 0);
@@ -561,12 +577,19 @@ void bdrv_subtree_drained_end(BlockDriverState *bs)
      BDRV_POLL_WHILE(bs, qatomic_read(&drained_end_counter) > 0);
  }
+void bdrv_subtree_drained_end_unlocked(BlockDriverState *bs)
+{
+    int drained_end_counter = 0;
+    bdrv_do_drained_end(bs, true, NULL, false, &drained_end_counter);
+    BDRV_POLL_WHILE_UNLOCKED(bs, qatomic_read(&drained_end_counter) > 0);
+}
+
  void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent)
  {
      int i;
for (i = 0; i < new_parent->recursive_quiesce_counter; i++) {
-        bdrv_do_drained_begin(child->bs, true, child, false, true);
+        bdrv_do_drained_begin(child->bs, true, child, false, true, false);
      }
  }
@@ -651,7 +674,8 @@ void bdrv_drain_all_begin(void)
      assert(qemu_in_main_thread());
if (qemu_in_coroutine()) {
-        bdrv_co_yield_to_drain(NULL, true, false, NULL, true, true, NULL);
+        bdrv_co_yield_to_drain(NULL, true, false, NULL, true, true, false,
+                               NULL);
          return;
      }
@@ -676,7 +700,7 @@ void bdrv_drain_all_begin(void)
          AioContext *aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
-        bdrv_do_drained_begin(bs, false, NULL, true, false);
+        bdrv_do_drained_begin(bs, false, NULL, true, false, false);
          aio_context_release(aio_context);
      }
diff --git a/include/block/block-io.h b/include/block/block-io.h
index 34a991649c..a329ae24c1 100644
--- a/include/block/block-io.h
+++ b/include/block/block-io.h
@@ -253,6 +253,7 @@ void bdrv_drained_begin_no_poll(BlockDriverState *bs);
   * exclusive access to all child nodes as well.
   */
  void bdrv_subtree_drained_begin(BlockDriverState *bs);
+void bdrv_subtree_drained_begin_unlocked(BlockDriverState *bs);
/**
   * bdrv_drained_end:
@@ -285,6 +286,7 @@ void bdrv_drained_end_no_poll(BlockDriverState *bs, int 
*drained_end_counter);
   * End a quiescent section started by bdrv_subtree_drained_begin().
   */
  void bdrv_subtree_drained_end(BlockDriverState *bs);
+void bdrv_subtree_drained_end_unlocked(BlockDriverState *bs);
bool bdrv_can_store_new_dirty_bitmap(BlockDriverState *bs, const char *name,
                                       uint32_t granularity, Error **errp);




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