gwj / at91sam9263 · Commits

Commit 0aa217e46124e873f75501f7187657e063f5903b

Authored by Kevin Wolf
Committed by Anthony Liguori
1 parent fc5b81d1

qcow2: Make cache=writethrough default 

The performance of qcow2 has improved meanwhile, so we don't need to
special-case it any more. Switch the default to write-through caching
like all other block drivers.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Inline Side-by-side
Showing 4 changed files with 3 additions and 16 deletions
... ... @@ -37,9 +37,8 @@ typedef struct QEMUSnapshotInfo {
37 37 bdrv_file_open()) */
38 38 #define BDRV_O_NOCACHE 0x0020 /* do not use the host page cache */
39 39 #define BDRV_O_CACHE_WB 0x0040 /* use write-back caching */
40   -#define BDRV_O_CACHE_DEF 0x0080 /* use default caching */
41 40  
42   -#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_CACHE_DEF)
  41 +#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)
43 42  
44 43 void bdrv_info(Monitor *mon);
45 44 void bdrv_info_stats(Monitor *mon);
... ...
block/qcow2.c
  View file @0aa217e
... ... @@ -145,14 +145,6 @@ static int qcow_open(BlockDriverState *bs, const char *filename, int flags)
145 145 QCowHeader header;
146 146 uint64_t ext_end;
147 147  
148   - /* Performance is terrible right now with cache=writethrough due mainly
149   - * to reference count updates. If the user does not explicitly specify
150   - * a caching type, force to writeback caching.
151   - */
152   - if ((flags & BDRV_O_CACHE_DEF)) {
153   - flags |= BDRV_O_CACHE_WB;
154   - flags &= ~BDRV_O_CACHE_DEF;
155   - }
156 148 ret = bdrv_file_open(&s->hd, filename, flags);
157 149 if (ret < 0)
158 150 return ret;
... ...
qemu-options.hx
  View file @0aa217e
... ... @@ -148,9 +148,7 @@ an internal copy of the data.
148 148  
149 149 Some block drivers perform badly with @option{cache=writethrough}, most notably,
150 150 qcow2. If performance is more important than correctness,
151   -@option{cache=writeback} should be used with qcow2. By default, if no explicit
152   -caching is specified for a qcow2 disk image, @option{cache=writeback} will be
153   -used. For all other disk types, @option{cache=writethrough} is the default.
  151 +@option{cache=writeback} should be used with qcow2.
154 152  
155 153 Instead of @option{-cdrom} you can use:
156 154 @example
... ...
... ... @@ -2239,7 +2239,7 @@ int drive_init(struct drive_opt *arg, int snapshot, void *opaque)
2239 2239 unit_id = -1;
2240 2240 translation = BIOS_ATA_TRANSLATION_AUTO;
2241 2241 index = -1;
2242   - cache = 3;
  2242 + cache = 1;
2243 2243  
2244 2244 if (machine->use_scsi) {
2245 2245 type = IF_SCSI;
... ... @@ -2557,8 +2557,6 @@ int drive_init(struct drive_opt *arg, int snapshot, void *opaque)
2557 2557 bdrv_flags |= BDRV_O_NOCACHE;
2558 2558 else if (cache == 2) /* write-back */
2559 2559 bdrv_flags |= BDRV_O_CACHE_WB;
2560   - else if (cache == 3) /* not specified */
2561   - bdrv_flags |= BDRV_O_CACHE_DEF;
2562 2560 if (bdrv_open2(bdrv, file, bdrv_flags, drv) < 0) {
2563 2561 fprintf(stderr, "qemu: could not open disk image %s\n",
2564 2562 file);
... ...