Re: [Qemu-devel] [PATCH v7 04/10] block: Support meta dirty bitmap

[Max Reitz]

On 18.07.2016 22:57, John Snow wrote:
> From: Fam Zheng <address@hidden>
> 
> The added group of operations enables tracking of the changed bits in
> the dirty bitmap.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>
> Signed-off-by: John Snow <address@hidden>
> ---
>  block/dirty-bitmap.c         | 52 
> ++++++++++++++++++++++++++++++++++++++++++++
>  include/block/dirty-bitmap.h |  9 ++++++++
>  2 files changed, 61 insertions(+)

[...]

> +int bdrv_dirty_bitmap_get_meta(BlockDriverState *bs,
> +                               BdrvDirtyBitmap *bitmap, int64_t sector,
> +                               int nb_sectors)
> +{
> +    uint64_t i;
> +    int gran = hbitmap_granularity(bitmap->meta);

/me is making a note first: If John says an optimization may be
premature, it probably is.

Did I say hbitmap_granularity()? I may have wanted to actually say
"1 << hbitmap_granularity()". Sorry. :-/

/me is making a second note now: Look up how something works before
proposing it, not after someone has actually followed your advice.

Max

> +
> +    /* To optimize: we can make hbitmap to internally check the range in a
> +     * coarse level, or at least do it word by word. */
> +    for (i = sector; i < sector + nb_sectors; i += gran) {
> +        if (hbitmap_get(bitmap->meta, i)) {
> +            return true;
> +        }
> +    }
> +    return false;
> +}

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