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 { @@ -37,9 +37,8 @@ typedef struct QEMUSnapshotInfo {
37 bdrv_file_open()) */ 37 bdrv_file_open()) */
38 #define BDRV_O_NOCACHE 0x0020 /* do not use the host page cache */ 38 #define BDRV_O_NOCACHE 0x0020 /* do not use the host page cache */
39 #define BDRV_O_CACHE_WB 0x0040 /* use write-back caching */ 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 void bdrv_info(Monitor *mon); 43 void bdrv_info(Monitor *mon);
45 void bdrv_info_stats(Monitor *mon); 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) @@ -145,14 +145,6 @@ static int qcow_open(BlockDriverState *bs, const char *filename, int flags)
145 QCowHeader header; 145 QCowHeader header;
146 uint64_t ext_end; 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 ret = bdrv_file_open(&s->hd, filename, flags); 148 ret = bdrv_file_open(&s->hd, filename, flags);
157 if (ret < 0) 149 if (ret < 0)
158 return ret; 150 return ret;
qemu-options.hx
  View file @0aa217e
@@ -148,9 +148,7 @@ an internal copy of the data. @@ -148,9 +148,7 @@ an internal copy of the data.
148 148
149 Some block drivers perform badly with @option{cache=writethrough}, most notably, 149 Some block drivers perform badly with @option{cache=writethrough}, most notably,
150 qcow2. If performance is more important than correctness, 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 Instead of @option{-cdrom} you can use: 153 Instead of @option{-cdrom} you can use:
156 @example 154 @example
@@ -2239,7 +2239,7 @@ int drive_init(struct drive_opt *arg, int snapshot, void *opaque) @@ -2239,7 +2239,7 @@ int drive_init(struct drive_opt *arg, int snapshot, void *opaque)
2239 unit_id = -1; 2239 unit_id = -1;
2240 translation = BIOS_ATA_TRANSLATION_AUTO; 2240 translation = BIOS_ATA_TRANSLATION_AUTO;
2241 index = -1; 2241 index = -1;
2242 - cache = 3; 2242 + cache = 1;
2243 2243
2244 if (machine->use_scsi) { 2244 if (machine->use_scsi) {
2245 type = IF_SCSI; 2245 type = IF_SCSI;
@@ -2557,8 +2557,6 @@ int drive_init(struct drive_opt *arg, int snapshot, void *opaque) @@ -2557,8 +2557,6 @@ int drive_init(struct drive_opt *arg, int snapshot, void *opaque)
2557 bdrv_flags |= BDRV_O_NOCACHE; 2557 bdrv_flags |= BDRV_O_NOCACHE;
2558 else if (cache == 2) /* write-back */ 2558 else if (cache == 2) /* write-back */
2559 bdrv_flags |= BDRV_O_CACHE_WB; 2559 bdrv_flags |= BDRV_O_CACHE_WB;
2560 - else if (cache == 3) /* not specified */  
2561 - bdrv_flags |= BDRV_O_CACHE_DEF;  
2562 if (bdrv_open2(bdrv, file, bdrv_flags, drv) < 0) { 2560 if (bdrv_open2(bdrv, file, bdrv_flags, drv) < 0) {
2563 fprintf(stderr, "qemu: could not open disk image %s\n", 2561 fprintf(stderr, "qemu: could not open disk image %s\n",
2564 file); 2562 file);