Re: fio offset with ba

[Sitsofe Wheeler <sitsofe@gmail.com>]

On 26 October 2017 at 05:24, Jens Axboe <axboe@kernel.dk> wrote:
> On 10/25/2017 05:27 PM, Jeff Furlong wrote:
>>> Actually here's a question - what does .interval do?
>> Looks like it is used to override the default value of 1 in gopt_new_int():
>>       interval = 1.0;
>>       if (o->interval)
>>               interval = o->interval;
>>       i->spin = gtk_spin_button_new_with_range(o->minval, maxval, interval);
>>
>> But your larger question may be why do some options have interval
>> (e.g. offset) and some not have interval (e.g. ioengine).
>
> It's for the GUI, where you want to specify in which increments a value
> is adjusted when you use the up and down arrows to change it. It's only
> applicable to numberical values, it would not make sense to apply to
> something like ioengine or similar.

You were right Jeff - it was a larger question. Jens thanks for
clearing up its purpose - I missed it was used by the GUI.

>> diff --git a/filesetup.c b/filesetup.c
>> index 7a602d4..5d7ea5c 100644
>> --- a/filesetup.c
>> +++ b/filesetup.c
>> @@ -869,12 +869,10 @@ uint64_t get_start_offset(struct thread_data *td, struct fio_file *f)
>>
>>       if (o->start_offset_percent > 0) {
>>               /*
>> -              * if blockalign is provided, find the min across read, write,
>> -              * and trim
>> +              * if offset_align is provided, set initial offset
>>                */
>> -             if (fio_option_is_set(o, ba)) {
>> -                     align_bs = (unsigned long long) min(o->ba[DDIR_READ], o->ba[DDIR_WRITE]);
>> -                     align_bs = min((unsigned long long) o->ba[DDIR_TRIM], align_bs);
>> +             if (fio_option_is_set(o, start_offset_align)) {
>> +                     align_bs = o->start_offset_align;
>
> I'm curious why this drops the 'ba' part?

blockalign actually only impacts random I/O (see
https://github.com/axboe/fio/issues/341 for someone requesting it to
affect sequential I/O but that's a separate issue). Since each random
I/O will "blockalign itself" we gain nothing from trying to align the
offset generated by offset percentage to it.

-- 
Sitsofe | http://sucs.org/~sits/