Il 22/06/2013 22:58, Peter Lieven ha scritto:
> this patch adds a efficient encoding for zero blocks by
> adding a new flag indiciating a block is completly zero.
>
> additionally bdrv_write_zeros() is used at the destination
> to efficiently write these zeroes. if the driver supports
> it this avoids blindly allocating all sectors consumed by
> zero blocks effectively re-thinning the device.
>
> Signed-off-by: Peter Lieven <p...@kamp.de>
This is a bit ugly because it doesn't work with drive-mirror. Perhaps
we can add a write-zeroes opcode to NBD, too.
Paolo
> ---
> block-migration.c | 29 +++++++++++++++++++++++------
> include/migration/qemu-file.h | 1 +
> savevm.c | 2 +-
> 3 files changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/block-migration.c b/block-migration.c
> index 2fd7699..99b3757 100644
> --- a/block-migration.c
> +++ b/block-migration.c
> @@ -29,6 +29,7 @@
> #define BLK_MIG_FLAG_DEVICE_BLOCK 0x01
> #define BLK_MIG_FLAG_EOS 0x02
> #define BLK_MIG_FLAG_PROGRESS 0x04
> +#define BLK_MIG_FLAG_ZERO_BLOCK 0x08
>
> #define MAX_IS_ALLOCATED_SEARCH 65536
>
> @@ -114,16 +115,29 @@ static void blk_mig_unlock(void)
> static void blk_send(QEMUFile *f, BlkMigBlock * blk)
> {
> int len;
> + int flags = BLK_MIG_FLAG_DEVICE_BLOCK;
> +
> + if (buffer_is_zero(blk->buf, BLOCK_SIZE)) {
> + flags |= BLK_MIG_FLAG_ZERO_BLOCK;
> + }
>
> /* sector number and flags */
> qemu_put_be64(f, (blk->sector << BDRV_SECTOR_BITS)
> - | BLK_MIG_FLAG_DEVICE_BLOCK);
> + | flags);
>
> /* device name */
> len = strlen(blk->bmds->bs->device_name);
> qemu_put_byte(f, len);
> qemu_put_buffer(f, (uint8_t *)blk->bmds->bs->device_name, len);
>
> + /* if a block is zero we need to flush here since the network
> + * bandwidth is now a lot higher than the storage device bandwidth.
> + * thus if we queue zero blocks we slow down the migration */
> + if (flags & BLK_MIG_FLAG_ZERO_BLOCK) {
> + qemu_fflush(f);
> + return;
> + }
> +
> qemu_put_buffer(f, blk->buf, BLOCK_SIZE);
> }
>
> @@ -762,12 +776,15 @@ static int block_load(QEMUFile *f, void *opaque, int
> version_id)
> nr_sectors = BDRV_SECTORS_PER_DIRTY_CHUNK;
> }
>
> - buf = g_malloc(BLOCK_SIZE);
> -
> - qemu_get_buffer(f, buf, BLOCK_SIZE);
> - ret = bdrv_write(bs, addr, buf, nr_sectors);
> + if (flags & BLK_MIG_FLAG_ZERO_BLOCK) {
> + ret = bdrv_write_zeroes(bs, addr, nr_sectors);
> + } else {
> + buf = g_malloc(BLOCK_SIZE);
> + qemu_get_buffer(f, buf, BLOCK_SIZE);
> + ret = bdrv_write(bs, addr, buf, nr_sectors);
> + g_free(buf);
> + }
>
> - g_free(buf);
> if (ret < 0) {
> return ret;
> }
> diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
> index 7519464..b73298d 100644
> --- a/include/migration/qemu-file.h
> +++ b/include/migration/qemu-file.h
> @@ -71,6 +71,7 @@ QEMUFile *qemu_fdopen(int fd, const char *mode);
> QEMUFile *qemu_fopen_socket(int fd, const char *mode);
> QEMUFile *qemu_popen_cmd(const char *command, const char *mode);
> int qemu_get_fd(QEMUFile *f);
> +void qemu_fflush(QEMUFile *f);
> int qemu_fclose(QEMUFile *f);
> int64_t qemu_ftell(QEMUFile *f);
> void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size);
> diff --git a/savevm.c b/savevm.c
> index ff5ece6..4d12d92 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -610,7 +610,7 @@ static inline bool qemu_file_is_writable(QEMUFile *f)
> * If there is writev_buffer QEMUFileOps it uses it otherwise uses
> * put_buffer ops.
> */
> -static void qemu_fflush(QEMUFile *f)
> +void qemu_fflush(QEMUFile *f)
> {
> ssize_t ret = 0;
>
>
