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[Qemu-block] [PULL 04/35] block: Add flag to avoid wasted work in bdrv_i
From: |
Kevin Wolf |
Subject: |
[Qemu-block] [PULL 04/35] block: Add flag to avoid wasted work in bdrv_is_allocated() |
Date: |
Thu, 26 Oct 2017 15:17:10 +0200 |
From: Eric Blake <address@hidden>
Not all callers care about which BDS owns the mapping for a given
range of the file, or where the zeroes lie within that mapping. In
particular, bdrv_is_allocated() cares more about finding the
largest run of allocated data from the guest perspective, whether
or not that data is consecutive from the host perspective, and
whether or not the data reads as zero. Therefore, doing subsequent
refinements such as checking how much of the format-layer
allocation also satisfies BDRV_BLOCK_ZERO at the protocol layer is
wasted work - in the best case, it just costs extra CPU cycles
during a single bdrv_is_allocated(), but in the worst case, it
results in a smaller *pnum, and forces callers to iterate through
more status probes when visiting the entire file for even more
extra CPU cycles.
This patch only optimizes the block layer (no behavior change when
want_zero is true, but skip unnecessary effort when it is false).
Then when subsequent patches tweak the driver callback to be
byte-based, we can also pass this hint through to the driver.
Tweak BdrvCoGetBlockStatusData to declare arguments in parameter
order, rather than mixing things up (minimizing padding is not
necessary here).
Signed-off-by: Eric Blake <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
---
block/io.c | 57 +++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 41 insertions(+), 16 deletions(-)
diff --git a/block/io.c b/block/io.c
index 93231b0e26..8ba408c813 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1769,10 +1769,11 @@ int bdrv_flush_all(void)
typedef struct BdrvCoGetBlockStatusData {
BlockDriverState *bs;
BlockDriverState *base;
- BlockDriverState **file;
+ bool want_zero;
int64_t sector_num;
int nb_sectors;
int *pnum;
+ BlockDriverState **file;
int64_t ret;
bool done;
} BdrvCoGetBlockStatusData;
@@ -1808,6 +1809,11 @@ int64_t coroutine_fn
bdrv_co_get_block_status_from_backing(BlockDriverState *bs,
* Drivers not implementing the functionality are assumed to not support
* backing files, hence all their sectors are reported as allocated.
*
+ * If 'want_zero' is true, the caller is querying for mapping purposes,
+ * and the result should include BDRV_BLOCK_OFFSET_VALID and
+ * BDRV_BLOCK_ZERO where possible; otherwise, the result may omit those
+ * bits particularly if it allows for a larger value in 'pnum'.
+ *
* If 'sector_num' is beyond the end of the disk image the return value is
* BDRV_BLOCK_EOF and 'pnum' is set to 0.
*
@@ -1824,6 +1830,7 @@ int64_t coroutine_fn
bdrv_co_get_block_status_from_backing(BlockDriverState *bs,
* is allocated in.
*/
static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
+ bool want_zero,
int64_t sector_num,
int nb_sectors, int *pnum,
BlockDriverState **file)
@@ -1878,31 +1885,34 @@ static int64_t coroutine_fn
bdrv_co_get_block_status(BlockDriverState *bs,
if (ret & BDRV_BLOCK_RAW) {
assert(ret & BDRV_BLOCK_OFFSET_VALID && local_file);
- ret = bdrv_co_get_block_status(local_file, ret >> BDRV_SECTOR_BITS,
+ ret = bdrv_co_get_block_status(local_file, want_zero,
+ ret >> BDRV_SECTOR_BITS,
*pnum, pnum, &local_file);
goto out;
}
if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {
ret |= BDRV_BLOCK_ALLOCATED;
- } else {
+ } else if (want_zero) {
if (bdrv_unallocated_blocks_are_zero(bs)) {
ret |= BDRV_BLOCK_ZERO;
} else if (bs->backing) {
BlockDriverState *bs2 = bs->backing->bs;
int64_t nb_sectors2 = bdrv_nb_sectors(bs2);
+
if (nb_sectors2 >= 0 && sector_num >= nb_sectors2) {
ret |= BDRV_BLOCK_ZERO;
}
}
}
- if (local_file && local_file != bs &&
+ if (want_zero && local_file && local_file != bs &&
(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO) &&
(ret & BDRV_BLOCK_OFFSET_VALID)) {
int file_pnum;
- ret2 = bdrv_co_get_block_status(local_file, ret >> BDRV_SECTOR_BITS,
+ ret2 = bdrv_co_get_block_status(local_file, want_zero,
+ ret >> BDRV_SECTOR_BITS,
*pnum, &file_pnum, NULL);
if (ret2 >= 0) {
/* Ignore errors. This is just providing extra information, it
@@ -1938,6 +1948,7 @@ early_out:
static int64_t coroutine_fn bdrv_co_get_block_status_above(BlockDriverState
*bs,
BlockDriverState *base,
+ bool want_zero,
int64_t sector_num,
int nb_sectors,
int *pnum,
@@ -1949,7 +1960,8 @@ static int64_t coroutine_fn
bdrv_co_get_block_status_above(BlockDriverState *bs,
assert(bs != base);
for (p = bs; p != base; p = backing_bs(p)) {
- ret = bdrv_co_get_block_status(p, sector_num, nb_sectors, pnum, file);
+ ret = bdrv_co_get_block_status(p, want_zero, sector_num, nb_sectors,
+ pnum, file);
if (ret < 0) {
break;
}
@@ -1979,6 +1991,7 @@ static void coroutine_fn
bdrv_get_block_status_above_co_entry(void *opaque)
BdrvCoGetBlockStatusData *data = opaque;
data->ret = bdrv_co_get_block_status_above(data->bs, data->base,
+ data->want_zero,
data->sector_num,
data->nb_sectors,
data->pnum,
@@ -1991,20 +2004,22 @@ static void coroutine_fn
bdrv_get_block_status_above_co_entry(void *opaque)
*
* See bdrv_co_get_block_status_above() for details.
*/
-int64_t bdrv_get_block_status_above(BlockDriverState *bs,
- BlockDriverState *base,
- int64_t sector_num,
- int nb_sectors, int *pnum,
- BlockDriverState **file)
+static int64_t bdrv_common_block_status_above(BlockDriverState *bs,
+ BlockDriverState *base,
+ bool want_zero,
+ int64_t sector_num,
+ int nb_sectors, int *pnum,
+ BlockDriverState **file)
{
Coroutine *co;
BdrvCoGetBlockStatusData data = {
.bs = bs,
.base = base,
- .file = file,
+ .want_zero = want_zero,
.sector_num = sector_num,
.nb_sectors = nb_sectors,
.pnum = pnum,
+ .file = file,
.done = false,
};
@@ -2020,6 +2035,16 @@ int64_t bdrv_get_block_status_above(BlockDriverState *bs,
return data.ret;
}
+int64_t bdrv_get_block_status_above(BlockDriverState *bs,
+ BlockDriverState *base,
+ int64_t sector_num,
+ int nb_sectors, int *pnum,
+ BlockDriverState **file)
+{
+ return bdrv_common_block_status_above(bs, base, true, sector_num,
+ nb_sectors, pnum, file);
+}
+
int64_t bdrv_get_block_status(BlockDriverState *bs,
int64_t sector_num,
int nb_sectors, int *pnum,
@@ -2032,15 +2057,15 @@ int64_t bdrv_get_block_status(BlockDriverState *bs,
int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
int64_t bytes, int64_t *pnum)
{
- int64_t sector_num = offset >> BDRV_SECTOR_BITS;
- int nb_sectors = bytes >> BDRV_SECTOR_BITS;
int64_t ret;
int psectors;
assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE) && bytes < INT_MAX);
- ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &psectors,
- NULL);
+ ret = bdrv_common_block_status_above(bs, backing_bs(bs), false,
+ offset >> BDRV_SECTOR_BITS,
+ bytes >> BDRV_SECTOR_BITS, &psectors,
+ NULL);
if (ret < 0) {
return ret;
}
--
2.13.6
- [Qemu-block] [PULL 00/35] Block layer patches, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 02/35] qemu-iotests: Test backing_fmt with backing node reference, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 01/35] block: don't add 'driver' to options when referring to backing via node name, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 03/35] block: Allow NULL file for bdrv_get_block_status(), Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 04/35] block: Add flag to avoid wasted work in bdrv_is_allocated(),
Kevin Wolf <=
- [Qemu-block] [PULL 05/35] block: Make bdrv_round_to_clusters() signature more useful, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 08/35] qemu-img: Switch get_block_status() to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 06/35] qcow2: Switch is_zero_sectors() to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 09/35] block: Convert bdrv_get_block_status() to bytes, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 07/35] block: Switch bdrv_make_zero() to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 11/35] block: Switch BdrvCoGetBlockStatusData to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 10/35] block: Switch bdrv_co_get_block_status() to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 12/35] block: Switch bdrv_common_block_status_above() to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 13/35] block: Switch bdrv_co_get_block_status_above() to byte-based, Kevin Wolf, 2017/10/26
- [Qemu-block] [PULL 15/35] qemu-img: Simplify logic in img_compare(), Kevin Wolf, 2017/10/26