Am 24.06.2013 16:32, schrieb Paolo Bonzini:
> 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.
That is the exact problem with NBD. If write zeroes is not supported
the routine falls back to write zeros with writev.
Peter
>
> 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;
>>
>>
