On 20.02.2014 18:18, Jens Axboe wrote:
> On Thu, Feb 20 2014, ehrhardt@xxxxxxxxxxxxxxxxxx wrote:
>> *Resend with hopefully non mangled patches*
>> References: <20140220131958.965092001@xxxxxxxxxxxxxxxxxx>
>> Content-Disposition: inline; filename=fix_last_block.diff
>>
>> From: Peter Oberparleiter <oberpar@xxxxxxxxxxxxxxxxxx>
>>
>> Fix the available range for random offsets which never touched the last block.
>>
>> Signed-off-by: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
>> ---
>> [diffstat]
>> io_u.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- a/io_u.c
>> +++ b/io_u.c
>> @@ -104,7 +104,7 @@ static int __get_next_rand_offset(struct
>>
>> dprint(FD_RANDOM, "off rand %llu\n", (unsigned long long) r);
>>
>> - *b = (lastb - 1) * (r / ((uint64_t) rmax + 1.0));
>> + *b = lastb * (r / ((uint64_t) rmax + 1.0));
>> } else {
>> uint64_t off = 0;
>
> Wont this generate lastb as the potentially last block? We want lastb-1
> as the last one, otherwise the length of IO from it will be 0.
>
> I might be missing something here.
I would expect that the last I/O would be at offset size-blocksize and
size blocksize. Consider this example test case that should generate 1
second of random reads with offsets 0 and 512:
[job]
filename=datafile
blocksize=512
size=1024
time_based
runtime=1
rw=randread
norandommap
write_iolog=/dev/stdout
Running it with FIO_VERSION = fio-2.1.5-44-ga1fc produces the following
result:
> fio job | grep datafile | sort | uniq
datafile add
datafile close
datafile open
datafile read 0 512
-> I/O is only generated for offset 0
Running it with the same version and the subject patch applied:
> fio job | grep datafile | sort | uniq
datafile add
datafile close
datafile open
datafile read 0 512
datafile read 512 512
-> Both offsets are covered
--
Peter Oberparleiter
Linux on System z Development - IBM Germany
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