Re: [Qemu-devel] [PATCH v2 1/3] block/backup: make backup cluster size configurable

[Fam Zheng <famz@redhat.com>]

On Mon, 02/22 17:07, John Snow wrote:
> 64K might not always be appropriate, make this a runtime value.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  block/backup.c | 64 +++++++++++++++++++++++++++++++++-------------------------
>  1 file changed, 36 insertions(+), 28 deletions(-)
> 
> diff --git a/block/backup.c b/block/backup.c
> index 00cafdb..76addef 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -21,10 +21,7 @@
>  #include "qemu/ratelimit.h"
>  #include "sysemu/block-backend.h"
>  
> -#define BACKUP_CLUSTER_BITS 16
> -#define BACKUP_CLUSTER_SIZE (1 << BACKUP_CLUSTER_BITS)
> -#define BACKUP_SECTORS_PER_CLUSTER (BACKUP_CLUSTER_SIZE / BDRV_SECTOR_SIZE)
> -
> +#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
>  #define SLICE_TIME 100000000ULL /* ns */
>  
>  typedef struct CowRequest {
> @@ -46,9 +43,16 @@ typedef struct BackupBlockJob {
>      CoRwlock flush_rwlock;
>      uint64_t sectors_read;
>      HBitmap *bitmap;
> +    int64_t cluster_size;
>      QLIST_HEAD(, CowRequest) inflight_reqs;
>  } BackupBlockJob;
>  
> +/* Size of a cluster in sectors, instead of bytes. */
> +static inline int64_t cluster_size_sectors(BackupBlockJob *job)
> +{
> +  return job->cluster_size / BDRV_SECTOR_SIZE;
> +}
> +
>  /* See if in-flight requests overlap and wait for them to complete */
>  static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
>                                                         int64_t start,
> @@ -97,13 +101,14 @@ static int coroutine_fn backup_do_cow(BlockDriverState *bs,
>      QEMUIOVector bounce_qiov;
>      void *bounce_buffer = NULL;
>      int ret = 0;
> +    int64_t sectors_per_cluster = cluster_size_sectors(job);
>      int64_t start, end;
>      int n;
>  
>      qemu_co_rwlock_rdlock(&job->flush_rwlock);
>  
> -    start = sector_num / BACKUP_SECTORS_PER_CLUSTER;
> -    end = DIV_ROUND_UP(sector_num + nb_sectors, BACKUP_SECTORS_PER_CLUSTER);
> +    start = sector_num / sectors_per_cluster;
> +    end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
>  
>      trace_backup_do_cow_enter(job, start, sector_num, nb_sectors);
>  
> @@ -118,12 +123,12 @@ static int coroutine_fn backup_do_cow(BlockDriverState *bs,
>  
>          trace_backup_do_cow_process(job, start);
>  
> -        n = MIN(BACKUP_SECTORS_PER_CLUSTER,
> +        n = MIN(sectors_per_cluster,
>                  job->common.len / BDRV_SECTOR_SIZE -
> -                start * BACKUP_SECTORS_PER_CLUSTER);
> +                start * sectors_per_cluster);
>  
>          if (!bounce_buffer) {
> -            bounce_buffer = qemu_blockalign(bs, BACKUP_CLUSTER_SIZE);
> +            bounce_buffer = qemu_blockalign(bs, job->cluster_size);
>          }
>          iov.iov_base = bounce_buffer;
>          iov.iov_len = n * BDRV_SECTOR_SIZE;
> @@ -131,10 +136,10 @@ static int coroutine_fn backup_do_cow(BlockDriverState *bs,
>  
>          if (is_write_notifier) {
>              ret = bdrv_co_readv_no_serialising(bs,
> -                                           start * BACKUP_SECTORS_PER_CLUSTER,
> +                                           start * sectors_per_cluster,
>                                             n, &bounce_qiov);
>          } else {
> -            ret = bdrv_co_readv(bs, start * BACKUP_SECTORS_PER_CLUSTER, n,
> +            ret = bdrv_co_readv(bs, start * sectors_per_cluster, n,
>                                  &bounce_qiov);
>          }
>          if (ret < 0) {
> @@ -147,11 +152,11 @@ static int coroutine_fn backup_do_cow(BlockDriverState *bs,
>  
>          if (buffer_is_zero(iov.iov_base, iov.iov_len)) {
>              ret = bdrv_co_write_zeroes(job->target,
> -                                       start * BACKUP_SECTORS_PER_CLUSTER,
> +                                       start * sectors_per_cluster,
>                                         n, BDRV_REQ_MAY_UNMAP);
>          } else {
>              ret = bdrv_co_writev(job->target,
> -                                 start * BACKUP_SECTORS_PER_CLUSTER, n,
> +                                 start * sectors_per_cluster, n,
>                                   &bounce_qiov);
>          }
>          if (ret < 0) {
> @@ -322,21 +327,22 @@ static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
>      int64_t cluster;
>      int64_t end;
>      int64_t last_cluster = -1;
> +    int64_t sectors_per_cluster = cluster_size_sectors(job);
>      BlockDriverState *bs = job->common.bs;
>      HBitmapIter hbi;
>  
>      granularity = bdrv_dirty_bitmap_granularity(job->sync_bitmap);
> -    clusters_per_iter = MAX((granularity / BACKUP_CLUSTER_SIZE), 1);
> +    clusters_per_iter = MAX((granularity / job->cluster_size), 1);
>      bdrv_dirty_iter_init(job->sync_bitmap, &hbi);
>  
>      /* Find the next dirty sector(s) */
>      while ((sector = hbitmap_iter_next(&hbi)) != -1) {
> -        cluster = sector / BACKUP_SECTORS_PER_CLUSTER;
> +        cluster = sector / sectors_per_cluster;
>  
>          /* Fake progress updates for any clusters we skipped */
>          if (cluster != last_cluster + 1) {
>              job->common.offset += ((cluster - last_cluster - 1) *
> -                                   BACKUP_CLUSTER_SIZE);
> +                                   job->cluster_size);
>          }
>  
>          for (end = cluster + clusters_per_iter; cluster < end; cluster++) {
> @@ -344,8 +350,8 @@ static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
>                  if (yield_and_check(job)) {
>                      return ret;
>                  }
> -                ret = backup_do_cow(bs, cluster * BACKUP_SECTORS_PER_CLUSTER,
> -                                    BACKUP_SECTORS_PER_CLUSTER, &error_is_read,
> +                ret = backup_do_cow(bs, cluster * sectors_per_cluster,
> +                                    sectors_per_cluster, &error_is_read,
>                                      false);
>                  if ((ret < 0) &&
>                      backup_error_action(job, error_is_read, -ret) ==
> @@ -357,17 +363,17 @@ static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
>  
>          /* If the bitmap granularity is smaller than the backup granularity,
>           * we need to advance the iterator pointer to the next cluster. */
> -        if (granularity < BACKUP_CLUSTER_SIZE) {
> -            bdrv_set_dirty_iter(&hbi, cluster * BACKUP_SECTORS_PER_CLUSTER);
> +        if (granularity < job->cluster_size) {
> +            bdrv_set_dirty_iter(&hbi, cluster * sectors_per_cluster);
>          }
>  
>          last_cluster = cluster - 1;
>      }
>  
>      /* Play some final catchup with the progress meter */
> -    end = DIV_ROUND_UP(job->common.len, BACKUP_CLUSTER_SIZE);
> +    end = DIV_ROUND_UP(job->common.len, job->cluster_size);
>      if (last_cluster + 1 < end) {
> -        job->common.offset += ((end - last_cluster - 1) * BACKUP_CLUSTER_SIZE);
> +        job->common.offset += ((end - last_cluster - 1) * job->cluster_size);
>      }
>  
>      return ret;
> @@ -384,13 +390,14 @@ static void coroutine_fn backup_run(void *opaque)
>          .notify = backup_before_write_notify,
>      };
>      int64_t start, end;
> +    int64_t sectors_per_cluster = cluster_size_sectors(job);
>      int ret = 0;
>  
>      QLIST_INIT(&job->inflight_reqs);
>      qemu_co_rwlock_init(&job->flush_rwlock);
>  
>      start = 0;
> -    end = DIV_ROUND_UP(job->common.len, BACKUP_CLUSTER_SIZE);
> +    end = DIV_ROUND_UP(job->common.len, job->cluster_size);
>  
>      job->bitmap = hbitmap_alloc(end, 0);
>  
> @@ -427,7 +434,7 @@ static void coroutine_fn backup_run(void *opaque)
>                  /* Check to see if these blocks are already in the
>                   * backing file. */
>  
> -                for (i = 0; i < BACKUP_SECTORS_PER_CLUSTER;) {
> +                for (i = 0; i < sectors_per_cluster;) {
>                      /* bdrv_is_allocated() only returns true/false based
>                       * on the first set of sectors it comes across that
>                       * are are all in the same state.
> @@ -436,8 +443,8 @@ static void coroutine_fn backup_run(void *opaque)
>                       * needed but at some point that is always the case. */
>                      alloced =
>                          bdrv_is_allocated(bs,
> -                                start * BACKUP_SECTORS_PER_CLUSTER + i,
> -                                BACKUP_SECTORS_PER_CLUSTER - i, &n);
> +                                start * sectors_per_cluster + i,
> +                                sectors_per_cluster - i, &n);
>                      i += n;
>  
>                      if (alloced == 1 || n == 0) {
> @@ -452,8 +459,8 @@ static void coroutine_fn backup_run(void *opaque)
>                  }
>              }
>              /* FULL sync mode we copy the whole drive. */
> -            ret = backup_do_cow(bs, start * BACKUP_SECTORS_PER_CLUSTER,
> -                    BACKUP_SECTORS_PER_CLUSTER, &error_is_read, false);
> +            ret = backup_do_cow(bs, start * sectors_per_cluster,
> +                                sectors_per_cluster, &error_is_read, false);
>              if (ret < 0) {
>                  /* Depending on error action, fail now or retry cluster */
>                  BlockErrorAction action =
> @@ -571,6 +578,7 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
>      job->sync_mode = sync_mode;
>      job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
>                         sync_bitmap : NULL;
> +    job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
>      job->common.len = len;
>      job->common.co = qemu_coroutine_create(backup_run);
>      block_job_txn_add_job(txn, &job->common);
> -- 
> 2.4.3
> 

Reviewed-by: Fam Zheng <famz@redhat.com>