Re: [Qemu-devel] [PATCHv3 1.8 8/9] qemu-img: increase min_sparse to 128 sectors (64kb)

[Peter Lieven]

Am 04.12.2013 17:43, schrieb Stefan Hajnoczi:
> On Wed, Nov 27, 2013 at 11:07:08AM +0100, Peter Lieven wrote:
>> Suggested-by: Paolo Bonzini <address@hidden>
>> Reviewed-by: Paolo Bonzini <address@hidden>
>> Signed-off-by: Peter Lieven <address@hidden>
>> ---
>>  qemu-img.c    |    4 ++--
>>  qemu-img.texi |    2 +-
>>  2 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/qemu-img.c b/qemu-img.c
>> index 9bb1f6f..8b5f3da 100644
>> --- a/qemu-img.c
>> +++ b/qemu-img.c
>> @@ -100,7 +100,7 @@ static void help(void)
>>             "  '-h' with or without a command shows this help and lists the 
>> supported formats\n"
>>             "  '-p' show progress of command (only certain commands)\n"
>>             "  '-q' use Quiet mode - do not print any output (except 
>> errors)\n"
>> -           "  '-S' indicates the consecutive number of bytes (defaults to 
>> 4k) that must\n"
>> +           "  '-S' indicates the consecutive number of bytes (defaults to 
>> 64k) that must\n"
>>             "       contain only zeros for qemu-img to create a sparse image 
>> during\n"
>>             "       conversion. If the number of bytes is 0, the source will 
>> not be scanned for\n"
>>             "       unallocated or zero sectors, and the destination image 
>> will always be\n"
>> @@ -1141,7 +1141,7 @@ static int img_convert(int argc, char **argv)
>>      QEMUOptionParameter *out_baseimg_param;
>>      char *options = NULL;
>>      const char *snapshot_name = NULL;
>> -    int min_sparse = 8; /* Need at least 4k of zeros for sparse detection */
>> +    int min_sparse = 128; /* Need at least 64k of zeros for sparse 
>> detection */
>>      bool quiet = false;
>>      Error *local_err = NULL;
> I guess a sane size would be cluster size.  For a raw file 4 KB is
> reasonable since that's the file system block size.
in case of iscsi the cluster size could be much too high as for example
my storage has a cluster_size of 15MB.
>
> Is it necessary to increase to 64 KB here?
No, its indepent of the rest. Paolo suggested to increase it and I can confirm
that for my usage case its faster than 4K.

I would drop this patch for now.

Peter