diff options
| author | aliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162> | 2008-12-04 21:39:21 +0000 |
|---|---|---|
| committer | aliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162> | 2008-12-04 21:39:21 +0000 |
| commit | 4dc822d726376fd4369089f04eb8605d2f94b74f (patch) | |
| tree | 743ea1d2ed14426c2d9f3da8d48d24b14f990df0 /block.h | |
| parent | 0cd2df75a2d7223b567c0eaa2547ce6c7d6a83f7 (diff) | |
Use writeback caching by default with qcow2
qcow2 writes a cluster reference count on every cluster update. This causes
performance to crater when using anything but cache=writeback. This is most
noticeable when using savevm. Right now, qcow2 isn't a reliable format
regardless of the type of cache your using because metadata is not updated in
the correct order. Considering this, I think it's somewhat reasonable to use
writeback caching by default with qcow2 files.
It at least avoids the massive performance regression for users until we sort
out the issues in qcow2.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5879 c046a42c-6fe2-441c-8c8c-71466251a162
Diffstat (limited to 'block.h')
| -rw-r--r-- | block.h | 3 |
1 files changed, 2 insertions, 1 deletions
@@ -49,8 +49,9 @@ typedef struct QEMUSnapshotInfo { bdrv_file_open()) */ #define BDRV_O_NOCACHE 0x0020 /* do not use the host page cache */ #define BDRV_O_CACHE_WB 0x0040 /* use write-back caching */ +#define BDRV_O_CACHE_DEF 0x0080 /* use default caching */ -#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_CACHE_WB) +#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_CACHE_DEF) void bdrv_info(void); void bdrv_info_stats(void); |