On 07/24/2018 07:17 AM, Leonid Bloch wrote:
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 <lbl...@janustech.com>
---
@@ -793,15 +800,32 @@ 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;
+ }
Since this makes the options mutually exclusive...
+++ b/qapi/block-core.json
@@ -2814,6 +2814,9 @@
# @l2-cache-size: the maximum size of the L2 table cache in
# bytes (since 2.2)
#
+# @l2-cache-full: make the L2 table cache large enough to cover the
+# entire image (since 3.1)
+#
...you should probably document that fact here.
+++ b/qemu-options.hx
@@ -758,6 +758,10 @@ The maximum total size of the L2 table and refcount block
caches in bytes
The maximum size of the L2 table cache in bytes
(default: 4/5 of the total cache size)
+@item l2-cache-full
+Make the L2 table cache large enough to cover the entire image
+(on/off; default: off)
Likewise.
+
@item refcount-cache-size
The maximum size of the refcount block cache in bytes
(default: 1/5 of the total cache size)
Alberto, looks like we missed this documentation in your changes to the
defaults.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
