Re: [Qemu-devel] [PATCH v3 12/20] mirror: Switch mirror_iteration() to byte-based

[Jeff Cody <jcody@redhat.com>]

On Tue, Jun 27, 2017 at 02:24:50PM -0500, Eric Blake wrote:
> We are gradually converting to byte-based interfaces, as they are
> easier to reason about than sector-based.  Change the internal
> loop iteration of mirroring to track by bytes instead of sectors
> (although we are still guaranteed that we iterate by steps that
> are both sector-aligned and multiples of the granularity).  Drop
> the now-unused mirror_clip_sectors().
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: John Snow <jsnow@redhat.com>
> 

Reviewed-by: Jeff Cody <jcody@redhat.com>

> ---
> v3: rebase to Paolo's thread-safety changes, R-b kept
> v2: straightforward rebase to earlier mirror_clip_bytes() change, R-b kept
> ---
>  block/mirror.c | 105 +++++++++++++++++++++++++--------------------------------
>  1 file changed, 46 insertions(+), 59 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 81ff784..0eb2af4 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -184,15 +184,6 @@ static inline int64_t mirror_clip_bytes(MirrorBlockJob *s,
>      return MIN(bytes, s->bdev_length - offset);
>  }
> 
> -/* Clip nb_sectors relative to sector_num to not exceed end-of-file */
> -static inline int mirror_clip_sectors(MirrorBlockJob *s,
> -                                      int64_t sector_num,
> -                                      int nb_sectors)
> -{
> -    return MIN(nb_sectors,
> -               s->bdev_length / BDRV_SECTOR_SIZE - sector_num);
> -}
> -
>  /* Round offset and/or bytes to target cluster if COW is needed, and
>   * return the offset of the adjusted tail against original. */
>  static int mirror_cow_align(MirrorBlockJob *s, int64_t *offset,
> @@ -336,30 +327,28 @@ static void mirror_do_zero_or_discard(MirrorBlockJob *s,
>  static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>  {
>      BlockDriverState *source = s->source;
> -    int64_t sector_num, first_chunk;
> +    int64_t offset, first_chunk;
>      uint64_t delay_ns = 0;
>      /* At least the first dirty chunk is mirrored in one iteration. */
>      int nb_chunks = 1;
> -    int64_t end = s->bdev_length / BDRV_SECTOR_SIZE;
>      int sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
>      bool write_zeroes_ok = bdrv_can_write_zeroes_with_unmap(blk_bs(s->target));
>      int max_io_bytes = MAX(s->buf_size / MAX_IN_FLIGHT, MAX_IO_BYTES);
> 
>      bdrv_dirty_bitmap_lock(s->dirty_bitmap);
> -    sector_num = bdrv_dirty_iter_next(s->dbi);
> -    if (sector_num < 0) {
> +    offset = bdrv_dirty_iter_next(s->dbi) * BDRV_SECTOR_SIZE;
> +    if (offset < 0) {
>          bdrv_set_dirty_iter(s->dbi, 0);
> -        sector_num = bdrv_dirty_iter_next(s->dbi);
> +        offset = bdrv_dirty_iter_next(s->dbi) * BDRV_SECTOR_SIZE;
>          trace_mirror_restart_iter(s, bdrv_get_dirty_count(s->dirty_bitmap) *
>                                    BDRV_SECTOR_SIZE);
> -        assert(sector_num >= 0);
> +        assert(offset >= 0);
>      }
>      bdrv_dirty_bitmap_unlock(s->dirty_bitmap);
> 
> -    first_chunk = sector_num / sectors_per_chunk;
> +    first_chunk = offset / s->granularity;
>      while (test_bit(first_chunk, s->in_flight_bitmap)) {
> -        trace_mirror_yield_in_flight(s, sector_num * BDRV_SECTOR_SIZE,
> -                                     s->in_flight);
> +        trace_mirror_yield_in_flight(s, offset, s->in_flight);
>          mirror_wait_for_io(s);
>      }
> 
> @@ -368,25 +357,26 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>      /* Find the number of consective dirty chunks following the first dirty
>       * one, and wait for in flight requests in them. */
>      bdrv_dirty_bitmap_lock(s->dirty_bitmap);
> -    while (nb_chunks * sectors_per_chunk < (s->buf_size >> BDRV_SECTOR_BITS)) {
> +    while (nb_chunks * s->granularity < s->buf_size) {
>          int64_t next_dirty;
> -        int64_t next_sector = sector_num + nb_chunks * sectors_per_chunk;
> -        int64_t next_chunk = next_sector / sectors_per_chunk;
> -        if (next_sector >= end ||
> -            !bdrv_get_dirty_locked(source, s->dirty_bitmap, next_sector)) {
> +        int64_t next_offset = offset + nb_chunks * s->granularity;
> +        int64_t next_chunk = next_offset / s->granularity;
> +        if (next_offset >= s->bdev_length ||
> +            !bdrv_get_dirty_locked(source, s->dirty_bitmap,
> +                                   next_offset >> BDRV_SECTOR_BITS)) {
>              break;
>          }
>          if (test_bit(next_chunk, s->in_flight_bitmap)) {
>              break;
>          }
> 
> -        next_dirty = bdrv_dirty_iter_next(s->dbi);
> -        if (next_dirty > next_sector || next_dirty < 0) {
> +        next_dirty = bdrv_dirty_iter_next(s->dbi) * BDRV_SECTOR_SIZE;
> +        if (next_dirty > next_offset || next_dirty < 0) {
>              /* The bitmap iterator's cache is stale, refresh it */
> -            bdrv_set_dirty_iter(s->dbi, next_sector);
> -            next_dirty = bdrv_dirty_iter_next(s->dbi);
> +            bdrv_set_dirty_iter(s->dbi, next_offset >> BDRV_SECTOR_BITS);
> +            next_dirty = bdrv_dirty_iter_next(s->dbi) * BDRV_SECTOR_SIZE;
>          }
> -        assert(next_dirty == next_sector);
> +        assert(next_dirty == next_offset);
>          nb_chunks++;
>      }
> 
> @@ -394,14 +384,15 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>       * calling bdrv_get_block_status_above could yield - if some blocks are
>       * marked dirty in this window, we need to know.
>       */
> -    bdrv_reset_dirty_bitmap_locked(s->dirty_bitmap, sector_num,
> -                                  nb_chunks * sectors_per_chunk);
> +    bdrv_reset_dirty_bitmap_locked(s->dirty_bitmap, offset >> BDRV_SECTOR_BITS,
> +                                   nb_chunks * sectors_per_chunk);
>      bdrv_dirty_bitmap_unlock(s->dirty_bitmap);
> 
> -    bitmap_set(s->in_flight_bitmap, sector_num / sectors_per_chunk, nb_chunks);
> -    while (nb_chunks > 0 && sector_num < end) {
> +    bitmap_set(s->in_flight_bitmap, offset / s->granularity, nb_chunks);
> +    while (nb_chunks > 0 && offset < s->bdev_length) {
>          int64_t ret;
>          int io_sectors;
> +        unsigned int io_bytes;
>          int64_t io_bytes_acct;
>          BlockDriverState *file;
>          enum MirrorMethod {
> @@ -410,28 +401,28 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>              MIRROR_METHOD_DISCARD
>          } mirror_method = MIRROR_METHOD_COPY;
> 
> -        assert(!(sector_num % sectors_per_chunk));
> -        ret = bdrv_get_block_status_above(source, NULL, sector_num,
> +        assert(!(offset % s->granularity));
> +        ret = bdrv_get_block_status_above(source, NULL,
> +                                          offset >> BDRV_SECTOR_BITS,
>                                            nb_chunks * sectors_per_chunk,
>                                            &io_sectors, &file);
> +        io_bytes = io_sectors * BDRV_SECTOR_SIZE;
>          if (ret < 0) {
> -            io_sectors = MIN(nb_chunks * sectors_per_chunk,
> -                             max_io_bytes >> BDRV_SECTOR_BITS);
> +            io_bytes = MIN(nb_chunks * s->granularity, max_io_bytes);
>          } else if (ret & BDRV_BLOCK_DATA) {
> -            io_sectors = MIN(io_sectors, max_io_bytes >> BDRV_SECTOR_BITS);
> +            io_bytes = MIN(io_bytes, max_io_bytes);
>          }
> 
> -        io_sectors -= io_sectors % sectors_per_chunk;
> -        if (io_sectors < sectors_per_chunk) {
> -            io_sectors = sectors_per_chunk;
> +        io_bytes -= io_bytes % s->granularity;
> +        if (io_bytes < s->granularity) {
> +            io_bytes = s->granularity;
>          } else if (ret >= 0 && !(ret & BDRV_BLOCK_DATA)) {
> -            int64_t target_sector_num;
> -            int target_nb_sectors;
> -            bdrv_round_sectors_to_clusters(blk_bs(s->target), sector_num,
> -                                           io_sectors,  &target_sector_num,
> -                                           &target_nb_sectors);
> -            if (target_sector_num == sector_num &&
> -                target_nb_sectors == io_sectors) {
> +            int64_t target_offset;
> +            unsigned int target_bytes;
> +            bdrv_round_to_clusters(blk_bs(s->target), offset, io_bytes,
> +                                   &target_offset, &target_bytes);
> +            if (target_offset == offset &&
> +                target_bytes == io_bytes) {
>                  mirror_method = ret & BDRV_BLOCK_ZERO ?
>                                      MIRROR_METHOD_ZERO :
>                                      MIRROR_METHOD_DISCARD;
> @@ -439,8 +430,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>          }
> 
>          while (s->in_flight >= MAX_IN_FLIGHT) {
> -            trace_mirror_yield_in_flight(s, sector_num * BDRV_SECTOR_SIZE,
> -                                         s->in_flight);
> +            trace_mirror_yield_in_flight(s, offset, s->in_flight);
>              mirror_wait_for_io(s);
>          }
> 
> @@ -448,30 +438,27 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>              return 0;
>          }
> 
> -        io_sectors = mirror_clip_sectors(s, sector_num, io_sectors);
> +        io_bytes = mirror_clip_bytes(s, offset, io_bytes);
>          switch (mirror_method) {
>          case MIRROR_METHOD_COPY:
> -            io_bytes_acct = mirror_do_read(s, sector_num * BDRV_SECTOR_SIZE,
> -                                           io_sectors * BDRV_SECTOR_SIZE);
> -            io_sectors = io_bytes_acct / BDRV_SECTOR_SIZE;
> +            io_bytes = io_bytes_acct = mirror_do_read(s, offset, io_bytes);
>              break;
>          case MIRROR_METHOD_ZERO:
>          case MIRROR_METHOD_DISCARD:
> -            mirror_do_zero_or_discard(s, sector_num * BDRV_SECTOR_SIZE,
> -                                      io_sectors * BDRV_SECTOR_SIZE,
> +            mirror_do_zero_or_discard(s, offset, io_bytes,
>                                        mirror_method == MIRROR_METHOD_DISCARD);
>              if (write_zeroes_ok) {
>                  io_bytes_acct = 0;
>              } else {
> -                io_bytes_acct = io_sectors * BDRV_SECTOR_SIZE;
> +                io_bytes_acct = io_bytes;
>              }
>              break;
>          default:
>              abort();
>          }
> -        assert(io_sectors);
> -        sector_num += io_sectors;
> -        nb_chunks -= DIV_ROUND_UP(io_sectors, sectors_per_chunk);
> +        assert(io_bytes);
> +        offset += io_bytes;
> +        nb_chunks -= DIV_ROUND_UP(io_bytes, s->granularity);
>          if (s->common.speed) {
>              delay_ns = ratelimit_calculate_delay(&s->limit, io_bytes_acct);
>          }
> -- 
> 2.9.4
>