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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>
This commit is contained in:
Kevin Wolf 2011-07-19 13:01:48 +02:00
parent 4a1d5e1fde
commit 93913dfd8a
3 changed files with 41 additions and 11 deletions
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12
block/qcow2-cache.c
View File

@ -312,3 +312,15 @@ found:
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;
}

38
block/qcow2-refcount.c
View File

@ -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;
}

2
block/qcow2.h
View File

@ -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);