Re: [Qemu-devel] [PATCH] block/iscsi: precache the allocation status of a target

[Peter Lieven <pl@kamp.de>]

Am 30.06.2016 um 17:59 schrieb Paolo Bonzini:
>
> On 30/06/2016 13:08, Peter Lieven wrote:
>> this fills up the allocationmap at iscsi_open. This helps
>> to reduce the number of get_block_status requests during runtime
>> significantly.
>>
>> Signed-off-by: Peter Lieven <pl@kamp.de>
>> ---
>>   block/iscsi.c | 16 ++++++++++++++++
>>   1 file changed, 16 insertions(+)
>>
>> diff --git a/block/iscsi.c b/block/iscsi.c
>> index 0cdcedb..04fb0a3 100644
>> --- a/block/iscsi.c
>> +++ b/block/iscsi.c
>> @@ -1774,6 +1774,22 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
>>                                        iscsilun->block_size) >> BDRV_SECTOR_BITS;
>>           if (iscsilun->lbprz) {
>>               ret = iscsi_allocmap_init(iscsilun, bs->open_flags);
>> +            if (ret == 0) {
>> +                unsigned int max_reqs = 64;
>> +                int64_t sector_num = 0;
>> +                while (max_reqs-- && sector_num < bs->total_sectors) {
>> +                    int n;
>> +                    BlockDriverState *file;
>> +                    ret = bdrv_get_block_status(bs, sector_num,
>> +                                                BDRV_REQUEST_MAX_SECTORS,
>> +                                                &n, &file);
>> +                    if (ret < 0) {
>> +                        break;
>> +                    }
>> +                    sector_num += n;
>> +                    ret = 0;
>> +                }
>> +            }
>>           }
>>       }
>>   
>>
> This can take a long time and the disks may not even be ever used.  I
> don't think it's a good idea.

Sure, the target might stay unused, but why do you suspect its slow?

Peter