Re: [Qemu-devel] [PATCH] block/iscsi: speed up read for unallocated sectors

[Peter Lieven <pl@kamp.de>]

Am 27.03.2014 15:17, schrieb Paolo Bonzini:
> Il 27/03/2014 14:43, Peter Lieven ha scritto:
>>
>> +static void iscsi_allocationmap_set(IscsiLun *iscsilun, int64_t sector_num,
>> +                                    int nb_sectors)
>> +{
>> +    if (!iscsilun->cluster_sectors) {
>> +        return;
>> +    }
>> +    bitmap_set(iscsilun->allocationmap,
>> +               sector_num / iscsilun->cluster_sectors,
>> +               DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
>> +}
>> +
>> +static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,
>> +                                      int nb_sectors)
>> +{
>> +    if (!iscsilun->cluster_sectors) {
>> +        return;
>> +    }
>> +    bitmap_clear(iscsilun->allocationmap,
>> +                 sector_num / iscsilun->cluster_sectors,
>> +                 DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
>> +}
>> +
>
> Here you need to round the other way, because partial clusters are not unmapped:
>
>     cluster_num = DIV_ROUND_UP(sector_num, iscsi->cluster_sectors);
>     nb_clusters = (sector_num + nb_sectors) / iscsi->cluster_sectors
>         - cluster_num;
>     bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);

Right, its not criticial because the allocationmap is more a hint, but its worth correcting
this. I have to check if bitmap_clear can cope with nb_clusters == 0.

thank you,
Peter

>
> Paolo