[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PULL 08/16] block: Reduce (un)drains when replacing a chil
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PULL 08/16] block: Reduce (un)drains when replacing a child |
Date: |
Fri, 16 Aug 2019 11:34:31 +0200 |
From: Max Reitz <address@hidden>
Currently, bdrv_replace_child_noperm() undrains the parent until it is
completely undrained, then re-drains it after attaching the new child
node.
This is a problem with bdrv_drop_intermediate(): We want to keep the
whole subtree drained, including parents, while the operation is
under way. bdrv_replace_child_noperm() breaks this by allowing every
parent to become unquiesced briefly, and then redraining it.
In fact, there is no reason why the parent should become unquiesced and
be allowed to submit requests to the new child node if that new node is
supposed to be kept drained. So if anything, we have to drain the
parent before detaching the old child node. Conversely, we have to
undrain it only after attaching the new child node.
Thus, change the whole drain algorithm here: Calculate the number of
times we have to drain/undrain the parent before replacing the child
node then drain it (if necessary), replace the child node, and then
undrain it.
Signed-off-by: Max Reitz <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
---
block.c | 49 +++++++++++++++++++++++++++++++++----------------
1 file changed, 33 insertions(+), 16 deletions(-)
diff --git a/block.c b/block.c
index df3407934b..66e8602e68 100644
--- a/block.c
+++ b/block.c
@@ -2230,13 +2230,27 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
BlockDriverState *new_bs)
{
BlockDriverState *old_bs = child->bs;
- int i;
+ int new_bs_quiesce_counter;
+ int drain_saldo;
assert(!child->frozen);
if (old_bs && new_bs) {
assert(bdrv_get_aio_context(old_bs) == bdrv_get_aio_context(new_bs));
}
+
+ new_bs_quiesce_counter = (new_bs ? new_bs->quiesce_counter : 0);
+ drain_saldo = new_bs_quiesce_counter - child->parent_quiesce_counter;
+
+ /*
+ * If the new child node is drained but the old one was not, flush
+ * all outstanding requests to the old child node.
+ */
+ while (drain_saldo > 0 && child->role->drained_begin) {
+ bdrv_parent_drained_begin_single(child, true);
+ drain_saldo--;
+ }
+
if (old_bs) {
/* Detach first so that the recursive drain sections coming from @child
* are already gone and we only end the drain sections that came from
@@ -2244,28 +2258,22 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
if (child->role->detach) {
child->role->detach(child);
}
- while (child->parent_quiesce_counter) {
- bdrv_parent_drained_end_single(child);
- }
QLIST_REMOVE(child, next_parent);
- } else {
- assert(child->parent_quiesce_counter == 0);
}
child->bs = new_bs;
if (new_bs) {
QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
- if (new_bs->quiesce_counter) {
- int num = new_bs->quiesce_counter;
- if (child->role->parent_is_bds) {
- num -= bdrv_drain_all_count;
- }
- assert(num >= 0);
- for (i = 0; i < num; i++) {
- bdrv_parent_drained_begin_single(child, true);
- }
- }
+
+ /*
+ * Detaching the old node may have led to the new node's
+ * quiesce_counter having been decreased. Not a problem, we
+ * just need to recognize this here and then invoke
+ * drained_end appropriately more often.
+ */
+ assert(new_bs->quiesce_counter <= new_bs_quiesce_counter);
+ drain_saldo += new_bs->quiesce_counter - new_bs_quiesce_counter;
/* Attach only after starting new drained sections, so that recursive
* drain sections coming from @child don't get an extra .drained_begin
@@ -2274,6 +2282,15 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
child->role->attach(child);
}
}
+
+ /*
+ * If the old child node was drained but the new one is not, allow
+ * requests to come in only after the new node has been attached.
+ */
+ while (drain_saldo < 0 && child->role->drained_end) {
+ bdrv_parent_drained_end_single(child);
+ drain_saldo++;
+ }
}
/*
--
2.20.1
- [Qemu-devel] [PULL 00/16] Block layer patches, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 01/16] iotests/118: Test media change for scsi-cd, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 02/16] iotests/118: Create test classes dynamically, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 04/16] iotests: Move migration helpers to iotests.py, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 03/16] iotests/118: Add -blockdev based tests, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 06/16] block: Simplify bdrv_filter_default_perms(), Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 08/16] block: Reduce (un)drains when replacing a child,
Kevin Wolf <=
- [Qemu-devel] [PULL 07/16] block: Keep subtree drained in drop_intermediate, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 05/16] iotests: Test migration with all kinds of filter nodes, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 09/16] tests: Test polling in bdrv_drop_intermediate(), Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 10/16] tests: Test mid-drain bdrv_replace_child_noperm(), Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 12/16] block: Remove blk_pread_unthrottled(), Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 11/16] iotests: Add test for concurrent stream/commit, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 13/16] mirror: Keep mirror_top_bs drained after dropping permissions, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 15/16] qemu-img convert: Deprecate using -n and -o together, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 14/16] block-backend: Queue requests while drained, Kevin Wolf, 2019/08/16
- [Qemu-devel] [PULL 16/16] file-posix: Handle undetectable alignment, Kevin Wolf, 2019/08/16