Re: [RFC PATCH 5/8] migration/dirtyrate: Compare hash results for recorded ramblock

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Chuan Zheng (zhengchuan@huawei.com) wrote:
> From: Zheng Chuan <zhengchuan@huawei.com>
> 
> Compare hash results for recorded ramblock.
> 
> Signed-off-by: Zheng Chuan <zhengchuan@huawei.com>
> Signed-off-by: YanYing Zhang <ann.zhuangyanying@huawei.com>
> ---
>  migration/dirtyrate.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 77 insertions(+)
> 
> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
> index 45cfc91..7badc53 100644
> --- a/migration/dirtyrate.c
> +++ b/migration/dirtyrate.c
> @@ -202,6 +202,83 @@ static int record_block_hash_info(struct dirtyrate_config config,
>      return 0;
>  }
>  
> +static int cal_block_dirty_rate(struct block_dirty_info *info)
> +{
> +    uint8_t *md = NULL;
> +    size_t hash_len;
> +    int i;
> +    int ret = 0;
> +
> +    hash_len = qcrypto_hash_digest_len(QCRYPTO_HASH_ALG_MD5);
> +    md = g_new0(uint8_t, hash_len);

Is 'hash_len' actually constant for a given algorithm, like MD5 ?
i.e. can we just have a nice fixed size array?

> +    for (i = 0; i < info->sample_pages_count; i++) {
> +        ret = get_block_vfn_hash(info, info->sample_page_vfn[i], &md, &hash_len);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +
> +        if (memcmp(md, info->hash_result + i * hash_len, hash_len) != 0) {
> +            info->sample_dirty_count++;

When the page doesn't match, do we have to update info->hash_result with
the new hash?   If the page is only modified once, and we catch it on
this cycle, we wouldn't want to catch it next time around.

> +        }
> +    }
> +
> +out:
> +    g_free(md);
> +    return ret;
> +}
> +
> +static bool find_block_matched(RAMBlock *block, struct block_dirty_info *infos,
> +                               int count, struct block_dirty_info **matched)
> +{
> +    int i;
> +
> +    for (i = 0; i < count; i++) {
> +        if (!strcmp(infos[i].idstr, qemu_ram_get_idstr(block))) {
> +            break;
> +        }
> +    }
> +
> +    if (i == count) {
> +        return false;
> +    }
> +
> +    if (infos[i].block_addr != qemu_ram_get_host_addr(block) ||
> +        infos[i].block_pages !=
> +            (qemu_ram_get_used_length(block) >> DIRTYRATE_PAGE_SIZE_SHIFT)) {

How does this happen?

> +        return false;
> +    }
> +
> +    *matched = &infos[i];
> +    return true;
> +}
> +
> +static int compare_block_hash_info(struct block_dirty_info *info, int block_index)
> +{
> +    struct block_dirty_info *block_dinfo = NULL;
> +    RAMBlock *block = NULL;
> +
> +    RAMBLOCK_FOREACH_MIGRATABLE(block) {
> +        if (ram_block_skip(block) < 0) {
> +            continue;
> +        }
> +        block_dinfo = NULL;
> +        if (!find_block_matched(block, info, block_index + 1, &block_dinfo)) {
> +            continue;
> +        }
> +        if (cal_block_dirty_rate(block_dinfo) < 0) {
> +            return -1;
> +        }
> +        update_dirtyrate_stat(block_dinfo);
> +    }
> +    if (!dirty_stat.total_sample_count) {
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +
>  static void calculate_dirtyrate(struct dirtyrate_config config, int64_t time)
>  {
>      /* todo */
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK