Permalink
Browse files

qcow2: Use Qcow2Cache in writeback mode during loadvm/savevm

In snapshotting there is no guest involved, so we can safely use a writeback
mode and do the flushes in the right place (i.e. at the very end). This
improves the time that creating/restoring an internal snapshot takes with an
image in writethrough mode.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
  • Loading branch information...
1 parent 4a1d5e1 commit 93913dfd8acbaddc8ef3716cd7b8a2830c99cb19 Kevin Wolf committed Jul 19, 2011
Showing with 41 additions and 11 deletions.
  1. +12 −0 block/qcow2-cache.c
  2. +27 −11 block/qcow2-refcount.c
  3. +2 −0 block/qcow2.h
View
@@ -312,3 +312,15 @@ void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table)
c->entries[i].dirty = true;
}
+bool qcow2_cache_set_writethrough(BlockDriverState *bs, Qcow2Cache *c,
+ bool enable)
+{
+ bool old = c->writethrough;
+
+ if (!old && enable) {
+ qcow2_cache_flush(bs, c);
+ }
+
+ c->writethrough = enable;
+ return old;
+}
View
@@ -705,8 +705,15 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
BDRVQcowState *s = bs->opaque;
uint64_t *l1_table, *l2_table, l2_offset, offset, l1_size2, l1_allocated;
int64_t old_offset, old_l2_offset;
- int i, j, l1_modified, nb_csectors, refcount;
+ int i, j, l1_modified = 0, nb_csectors, refcount;
int ret;
+ bool old_l2_writethrough, old_refcount_writethrough;
+
+ /* Switch caches to writeback mode during update */
+ old_l2_writethrough =
+ qcow2_cache_set_writethrough(bs, s->l2_table_cache, false);
+ old_refcount_writethrough =
+ qcow2_cache_set_writethrough(bs, s->refcount_block_cache, false);
l2_table = NULL;
l1_table = NULL;
@@ -720,7 +727,11 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
l1_allocated = 1;
if (bdrv_pread(bs->file, l1_table_offset,
l1_table, l1_size2) != l1_size2)
+ {
+ ret = -EIO;
goto fail;
+ }
+
for(i = 0;i < l1_size; i++)
be64_to_cpus(&l1_table[i]);
} else {
@@ -729,7 +740,6 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
l1_allocated = 0;
}
- l1_modified = 0;
for(i = 0; i < l1_size; i++) {
l2_offset = l1_table[i];
if (l2_offset) {
@@ -773,6 +783,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
}
if (refcount < 0) {
+ ret = -EIO;
goto fail;
}
}
@@ -803,6 +814,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
refcount = get_refcount(bs, l2_offset >> s->cluster_bits);
}
if (refcount < 0) {
+ ret = -EIO;
goto fail;
} else if (refcount == 1) {
l2_offset |= QCOW_OFLAG_COPIED;
@@ -813,6 +825,18 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
}
}
}
+
+ ret = 0;
+fail:
+ if (l2_table) {
+ qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
+ }
+
+ /* Enable writethrough cache mode again */
+ qcow2_cache_set_writethrough(bs, s->l2_table_cache, old_l2_writethrough);
+ qcow2_cache_set_writethrough(bs, s->refcount_block_cache,
+ old_refcount_writethrough);
+
if (l1_modified) {
for(i = 0; i < l1_size; i++)
cpu_to_be64s(&l1_table[i]);
@@ -824,15 +848,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
}
if (l1_allocated)
qemu_free(l1_table);
- return 0;
- fail:
- if (l2_table) {
- qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
- }
-
- if (l1_allocated)
- qemu_free(l1_table);
- return -EIO;
+ return ret;
}
View
@@ -228,6 +228,8 @@ int qcow2_read_snapshots(BlockDriverState *bs);
Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables,
bool writethrough);
int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache *c);
+bool qcow2_cache_set_writethrough(BlockDriverState *bs, Qcow2Cache *c,
+ bool enable);
void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table);
int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c);

0 comments on commit 93913df

Please sign in to comment.