@@ -695,6 +695,11 @@ static QemuOptsList qcow2_runtime_opts = {
.type = QEMU_OPT_SIZE,
.help = "Maximum L2 table cache size",
},
+ {
+ .name = QCOW2_OPT_L2_CACHE_FULL,
+ .type = QEMU_OPT_BOOL,
+ .help = "Create full coverage of the image with the L2 cache",
+ },
{
.name = QCOW2_OPT_L2_CACHE_ENTRY_SIZE,
.type = QEMU_OPT_SIZE,
@@ -779,10 +784,12 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
BDRVQcow2State *s = bs->opaque;
uint64_t combined_cache_size;
bool l2_cache_size_set, refcount_cache_size_set, combined_cache_size_set;
+ bool l2_cache_full_set;
int min_refcount_cache = MIN_REFCOUNT_CACHE_SIZE * s->cluster_size;
combined_cache_size_set = qemu_opt_get(opts, QCOW2_OPT_CACHE_SIZE);
l2_cache_size_set = qemu_opt_get(opts, QCOW2_OPT_L2_CACHE_SIZE);
+ l2_cache_full_set = qemu_opt_get(opts, QCOW2_OPT_L2_CACHE_FULL);
refcount_cache_size_set = qemu_opt_get(opts, QCOW2_OPT_REFCOUNT_CACHE_SIZE);
combined_cache_size = qemu_opt_get_size(opts, QCOW2_OPT_CACHE_SIZE, 0);
@@ -793,6 +800,17 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
*l2_cache_entry_size = qemu_opt_get_size(
opts, QCOW2_OPT_L2_CACHE_ENTRY_SIZE, s->cluster_size);
+ uint64_t virtual_disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
+ uint64_t max_l2_cache = virtual_disk_size / (s->cluster_size / 8);
+
+ if (l2_cache_size_set && l2_cache_full_set) {
+ error_setg(errp, QCOW2_OPT_L2_CACHE_SIZE " and "
+ QCOW2_OPT_L2_CACHE_FULL " may not be set at the same time");
+ return;
+ } else if (l2_cache_full_set) {
+ *l2_cache_size = max_l2_cache;
+ }
+
if (combined_cache_size_set) {
if (l2_cache_size_set && refcount_cache_size_set) {
error_setg(errp, QCOW2_OPT_CACHE_SIZE ", " QCOW2_OPT_L2_CACHE_SIZE
@@ -800,8 +818,14 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
"at the same time");
return;
} else if (*l2_cache_size > combined_cache_size) {
- error_setg(errp, QCOW2_OPT_L2_CACHE_SIZE " may not exceed "
- QCOW2_OPT_CACHE_SIZE);
+ if (l2_cache_full_set) {
+ error_setg(errp, QCOW2_OPT_CACHE_SIZE " must be greater than "
+ "the full L2 cache if " QCOW2_OPT_L2_CACHE_FULL
+ " is used");
+ } else {
+ error_setg(errp, QCOW2_OPT_L2_CACHE_SIZE " may not exceed "
+ QCOW2_OPT_CACHE_SIZE);
+ }
return;
} else if (*refcount_cache_size > combined_cache_size) {
error_setg(errp, QCOW2_OPT_REFCOUNT_CACHE_SIZE " may not exceed "
@@ -809,14 +833,11 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
return;
}
- if (l2_cache_size_set) {
+ if (l2_cache_size_set || l2_cache_full_set) {
*refcount_cache_size = combined_cache_size - *l2_cache_size;
} else if (refcount_cache_size_set) {
*l2_cache_size = combined_cache_size - *refcount_cache_size;
} else {
- uint64_t virtual_disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
- uint64_t max_l2_cache = virtual_disk_size / (s->cluster_size / 8);
-
/* Assign as much memory as possible to the L2 cache, and
* use the remainder for the refcount cache */
if (combined_cache_size >= max_l2_cache + min_refcount_cache) {
@@ -829,7 +850,7 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
}
}
} else {
- if (!l2_cache_size_set) {
+ if (!l2_cache_size_set && !l2_cache_full_set) {
*l2_cache_size = MAX(DEFAULT_L2_CACHE_BYTE_SIZE,
(uint64_t)DEFAULT_L2_CACHE_CLUSTERS
* s->cluster_size);
@@ -97,6 +97,7 @@
#define QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY "overlap-check.bitmap-directory"
#define QCOW2_OPT_CACHE_SIZE "cache-size"
#define QCOW2_OPT_L2_CACHE_SIZE "l2-cache-size"
+#define QCOW2_OPT_L2_CACHE_FULL "l2-cache-full"
#define QCOW2_OPT_L2_CACHE_ENTRY_SIZE "l2-cache-entry-size"
#define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
#define QCOW2_OPT_CACHE_CLEAN_INTERVAL "cache-clean-interval"
@@ -110,11 +110,12 @@ How to configure the cache sizes
Cache sizes can be configured using the -drive option in the
command-line, or the 'blockdev-add' QMP command.
-There are three options available, and all of them take bytes:
+There are four options available:
-"l2-cache-size": maximum size of the L2 table cache
-"refcount-cache-size": maximum size of the refcount block cache
-"cache-size": maximum size of both caches combined
+"l2-cache-size": maximum size of the L2 table cache (bytes, K, M)
+"refcount-cache-size": maximum size of the refcount block cache (bytes, K, M)
+"cache-size": maximum size of both caches combined (bytes, K, M)
+"l2-cache-full": make the L2 cache cover the full image (boolean)
There are a few things that need to be taken into account:
@@ -130,6 +131,12 @@ There are a few things that need to be taken into account:
memory as possible to the L2 cache before increasing the refcount
cache size.
+- If "l2-cache-full" is specified, QEMU will assign enough memory
+ to the L2 cache to cover the entire size of the image.
+
+- "l2-cache-size" and "l2-cache-full" can not be set simultaneously, as
+ setting "l2-cache-full" already implies a specific size for the L2 cache.
+
- At most two of "l2-cache-size", "refcount-cache-size", and "cache-size"
can be set simultaneously.
@@ -2812,7 +2812,12 @@
# refcount block caches in bytes (since 2.2)
#
# @l2-cache-size: the maximum size of the L2 table cache in
-# bytes (since 2.2)
+# bytes (mutually exclusive with l2-cache-full)
+# (since 2.2)
+#
+# @l2-cache-full: make the L2 table cache large enough to cover the
+# entire image (mutually exclusive with l2-cache-size)
+# (since 3.1)
#
# @l2-cache-entry-size: the size of each entry in the L2 cache in
# bytes. It must be a power of two between 512
@@ -2840,6 +2845,7 @@
'*overlap-check': 'Qcow2OverlapChecks',
'*cache-size': 'int',
'*l2-cache-size': 'int',
+ '*l2-cache-full': 'bool',
'*l2-cache-entry-size': 'int',
'*refcount-cache-size': 'int',
'*cache-clean-interval': 'int',
@@ -754,11 +754,15 @@ image file)
The maximum total size of the L2 table and refcount block caches in bytes
@item l2-cache-size
-The maximum size of the L2 table cache.
+The maximum size of the L2 table cache. (Mutually exclusive with l2-cache-full)
(default: if cache-size is not defined - 1048576 bytes or 8 clusters, whichever
is larger; otherwise, as large as possible or needed within the cache-size,
while permitting the requested or the minimal refcount cache size)
+@item l2-cache-full
+Make the L2 table cache large enough to cover the entire image (mutually
+exclusive with l2-cache-size) (on/off; default: off)
+
@item refcount-cache-size
The maximum size of the refcount block cache in bytes
(default: 4 times the cluster size, or any portion of the cache-size, if it is
An option "l2-cache-full" is introduced to automatically set the qcow2 L2 cache to a sufficient value for covering the entire image. The memory overhead when using this option is not big (1 MB for each 8 GB of virtual image size with the default cluster size) and it can noticeably improve performance when using large images with frequent I/O. Previously, for this functionality the correct L2 cache size needed to be calculated manually or with a script, and then this size needed to be passed to the "l2-cache-size" option. Now it is sufficient to just pass the boolean "l2-cache-full" option. Signed-off-by: Leonid Bloch <lbloch@janustech.com> --- block/qcow2.c | 35 ++++++++++++++++++++++++++++------- block/qcow2.h | 1 + docs/qcow2-cache.txt | 15 +++++++++++---- qapi/block-core.json | 8 +++++++- qemu-options.hx | 6 +++++- 5 files changed, 52 insertions(+), 13 deletions(-)