Re: [Qemu-devel] [PATCH v5 07/10] hbitmap: serialization

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

On 03.06.2016 07:32, Fam Zheng wrote:
> From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>
> Functions to serialize / deserialize(restore) HBitmap. HBitmap should be
> saved to linear sequence of bits independently of endianness and bitmap
> array element (unsigned long) size. Therefore Little Endian is chosen.
>
> These functions are appropriate for dirty bitmap migration, restoring
> the bitmap in several steps is available. To save performance, every
> step writes only the last level of the bitmap. All other levels are
> restored by hbitmap_deserialize_finish() as a last step of restoring.
> So, HBitmap is inconsistent while restoring.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> [Fix left shift operand to 1UL; add "finish" parameter. - Fam]
> Signed-off-by: Fam Zheng <famz@redhat.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>   include/qemu/hbitmap.h |  79 ++++++++++++++++++++++++++++
>   util/hbitmap.c         | 137 +++++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 216 insertions(+)
>
> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
> index f8ed058..26cac7d 100644
> --- a/include/qemu/hbitmap.h
> +++ b/include/qemu/hbitmap.h
> @@ -146,6 +146,85 @@ void hbitmap_reset_all(HBitmap *hb);
>   bool hbitmap_get(const HBitmap *hb, uint64_t item);
>   
>   /**
> + * hbitmap_serialization_granularity:
> + * @hb: HBitmap to operate on.
> + *
> + * Granularity of serialization chunks, used by other serialization functions.
> + * For every chunk:
> + * 1. Chunk start should be aligned to this granularity.
> + * 2. Chunk size should be aligned too, except for last chunk (for which
> + *      start + count == hb->size)
> + */
> +uint64_t hbitmap_serialization_granularity(const HBitmap *hb);
> +
> +/**
> + * hbitmap_serialization_size:
> + * @hb: HBitmap to operate on.
> + * @start: Starting bit
> + * @count: Number of bits
> + *
> + * Return number of bytes hbitmap_(de)serialize_part needs
> + */
> +uint64_t hbitmap_serialization_size(const HBitmap *hb,
> +                                    uint64_t start, uint64_t count);
> +
> +/**
> + * hbitmap_serialize_part
> + * @hb: HBitmap to operate on.
> + * @buf: Buffer to store serialized bitmap.
> + * @start: First bit to store.
> + * @count: Number of bits to store.
> + *
> + * Stores HBitmap data corresponding to given region. The format of saved data
> + * is linear sequence of bits, so it can be used by hbitmap_deserialize_part
> + * independently of endianness and size of HBitmap level array elements
> + */
> +void hbitmap_serialize_part(const HBitmap *hb, uint8_t *buf,
> +                            uint64_t start, uint64_t count);
> +
> +/**
> + * hbitmap_deserialize_part
> + * @hb: HBitmap to operate on.
> + * @buf: Buffer to restore bitmap data from.
> + * @start: First bit to restore.
> + * @count: Number of bits to restore.
> + * @finish: Whether to call hbitmap_deserialize_finish automatically.
> + *
> + * Restores HBitmap data corresponding to given region. The format is the same
> + * as for hbitmap_serialize_part.
> + *
> + * If @finish is false, caller must call hbitmap_serialize_finish before using
> + * the bitmap.
> + */
> +void hbitmap_deserialize_part(HBitmap *hb, uint8_t *buf,
> +                              uint64_t start, uint64_t count,
> +                              bool finish);
> +
> +/**
> + * hbitmap_deserialize_zeroes
> + * @hb: HBitmap to operate on.
> + * @start: First bit to restore.
> + * @count: Number of bits to restore.
> + * @finish: Whether to call hbitmap_deserialize_finish automatically.
> + *
> + * Fills the bitmap with zeroes.
> + *
> + * If @finish is false, caller must call hbitmap_serialize_finish before using
> + * the bitmap.
> + */
> +void hbitmap_deserialize_zeroes(HBitmap *hb, uint64_t start, uint64_t count,
> +                                bool finish);
> +
> +/**
> + * hbitmap_deserialize_finish
> + * @hb: HBitmap to operate on.
> + *
> + * Repair HBitmap after calling hbitmap_deserialize_data. Actually, all HBitmap
> + * layers are restored here.
> + */
> +void hbitmap_deserialize_finish(HBitmap *hb);
> +
> +/**
>    * hbitmap_free:
>    * @hb: HBitmap to operate on.
>    *
> diff --git a/util/hbitmap.c b/util/hbitmap.c
> index 13c0df5..70dc99b 100644
> --- a/util/hbitmap.c
> +++ b/util/hbitmap.c
> @@ -395,6 +395,143 @@ bool hbitmap_get(const HBitmap *hb, uint64_t item)
>       return (hb->levels[HBITMAP_LEVELS - 1][pos >> BITS_PER_LEVEL] & bit) != 0;
>   }
>   
> +uint64_t hbitmap_serialization_granularity(const HBitmap *hb)
> +{
> +    /* Require at least 64 bit granularity to be safe on both 64 bit and 32 bit
> +     * hosts. */
> +    return 64 << hb->granularity;
> +}
> +
> +/* Start should be aligned to serialization granularity, chunk size should be
> + * aligned to serialization granularity too, except for last chunk.
> + */
> +static void serialization_chunk(const HBitmap *hb,
> +                                uint64_t start, uint64_t count,
> +                                unsigned long **first_el, size_t *el_count)
> +{
> +    uint64_t last = start + count - 1;
> +    uint64_t gran = hbitmap_serialization_granularity(hb);
> +
> +    assert((start & (gran - 1)) == 0);
> +    assert((last >> hb->granularity) < hb->size);
> +    if ((last >> hb->granularity) != hb->size - 1) {
> +        assert((count & (gran - 1)) == 0);
> +    }
> +
> +    start = (start >> hb->granularity) >> BITS_PER_LEVEL;
> +    last = (last >> hb->granularity) >> BITS_PER_LEVEL;
> +
> +    *first_el = &hb->levels[HBITMAP_LEVELS - 1][start];
> +    *el_count = last - start + 1;
> +}
> +
> +uint64_t hbitmap_serialization_size(const HBitmap *hb,
> +                                    uint64_t start, uint64_t count)
> +{
> +    uint64_t el_count;
> +    unsigned long *cur;
> +
> +    if (!count) {
> +        return 0;
> +    }
> +    serialization_chunk(hb, start, count, &cur, &el_count);
> +
> +    return el_count * sizeof(unsigned long);
> +}
> +
> +void hbitmap_serialize_part(const HBitmap *hb, uint8_t *buf,
> +                            uint64_t start, uint64_t count)
> +{
> +    uint64_t el_count;
> +    unsigned long *cur, *end;
> +
> +    if (!count) {
> +        return;
> +    }
> +    serialization_chunk(hb, start, count, &cur, &el_count);
> +    end = cur + el_count;
> +

I think it would be better to memcpy the whole part and then loop with 
cpu_to_le64. This loop will go out from compilation for LE case (I 
hope), so in LE case it would be just one memcpy. However in BE case it 
should be better to memcpy large part first and then convert words.
> +    while (cur != end) {
> +        unsigned long el =
> +            (BITS_PER_LONG == 32 ? cpu_to_le32(*cur) : cpu_to_le64(*cur));
> +
> +        memcpy(buf, &el, sizeof(el));
> +        buf += sizeof(el);
> +        cur++;
> +    }
> +}
> +
> +void hbitmap_deserialize_part(HBitmap *hb, uint8_t *buf,
> +                              uint64_t start, uint64_t count,
> +                              bool finish)
> +{
> +    uint64_t el_count;
> +    unsigned long *cur, *end;
> +
> +    if (!count) {
> +        return;
> +    }
> +    serialization_chunk(hb, start, count, &cur, &el_count);
> +    end = cur + el_count;
> +

the same here.
> +    while (cur != end) {
> +        memcpy(cur, buf, sizeof(*cur));
> +
> +        if (BITS_PER_LONG == 32) {
> +            le32_to_cpus((uint32_t *)cur);
> +        } else {
> +            le64_to_cpus((uint64_t *)cur);
> +        }
> +
> +        buf += sizeof(unsigned long);
> +        cur++;
> +    }
> +    if (finish) {
> +        hbitmap_deserialize_finish(hb);
> +    }
> +}
> +
> +void hbitmap_deserialize_zeroes(HBitmap *hb, uint64_t start, uint64_t count,
> +                                bool finish)
> +{
> +    uint64_t el_count;
> +    unsigned long *first;
> +
> +    if (!count) {
> +        return;
> +    }
> +    serialization_chunk(hb, start, count, &first, &el_count);
> +
> +    memset(first, 0, el_count * sizeof(unsigned long));
> +    if (finish) {
> +        hbitmap_deserialize_finish(hb);
> +    }
> +}
> +
> +void hbitmap_deserialize_finish(HBitmap *bitmap)
> +{
> +    int64_t i, size, prev_size;
> +    int lev;
> +
> +    /* restore levels starting from penultimate to zero level, assuming
> +     * that the last level is ok */
> +    size = MAX((bitmap->size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
> +    for (lev = HBITMAP_LEVELS - 1; lev-- > 0; ) {
> +        prev_size = size;
> +        size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
> +        memset(bitmap->levels[lev], 0, size * sizeof(unsigned long));
> +
> +        for (i = 0; i < prev_size; ++i) {
> +            if (bitmap->levels[lev + 1][i]) {
> +                bitmap->levels[lev][i >> BITS_PER_LEVEL] |=
> +                    1UL << (i & (BITS_PER_LONG - 1));
> +            }
> +        }
> +    }
> +
> +    bitmap->levels[0][0] |= 1UL << (BITS_PER_LONG - 1);
> +}
> +
>   void hbitmap_free(HBitmap *hb)
>   {
>       unsigned i;


-- 
Best regards,
Vladimir