Re: Random distribution: zoned argument

[Jens Axboe <axboe@kernel.dk>]

We can add empty zones, that's fine, if that already doesn't work.

For your case, can you try and kill this line:

        qsort(o->zone_split[ddir], o->zone_split_nr[ddir], sizeof(struct zone_split), zone_cmp);

in options.c:zone_split_ddir(), I have a feeling that's screwing us over.


On 11/27/2017 04:18 PM, Phillip Chen wrote:
> I agree that changing the zoned random distribution parameter to allow
> absolute sizes would be an elegant way to address my use case. I'm not
> sure if it would be easier to add that functionality to the zoned
> distribution or create a new distribution named something like
> zoned_sectors. I'd also like the ability to have zones that no I/O
> will fall into. I think the easiest way to do that would be to allow 0
> as a valid distribution percentage (I.E. something like
> random_distribution=zoned:10/10:0/50:30/20:8/30:2/40). Currently it
> seems I can specify 0 as a distribution percentage, but it doesn't
> create a zero I/O zone like I would like it to. Although that might be
> addressed just by making the zoned distribution randomize I/O as
> expected.
> Thanks for looking into this,
> Phillip Chen
> 
> On Mon, Nov 20, 2017 at 6:57 PM, Jens Axboe <axboe@kernel.dk> wrote:
>> On 11/20/2017 10:17 AM, Phillip Chen wrote:
>>> Hello,
>>> I'm a test engineer at Seagate and we're using FIO to gather some
>>> performance data. This email has two parts: a bug report and a feature
>>> request.
>>> The bug that I'm seeing is that when using the
>>> random_distribution=zoned argument, the zone order is not honored. So
>>> using zoned:18/90:7/5:75/5 will not weight IO towards the end of the
>>> disk but rather towards the beginning. Using zoned:75/5:7/5:18/90
>>> apparently gives the same distribution, but also not the correct
>>> distribution. I've attached a python3.6 script that shows this
>>> behaviour. Here is the histogram information from running the two
>>> zoned arguments as described above:
>>>
>>> Using fio --name=rand_reads --ioengine=libaio --direct=1 --exitall
>>> --thread --filename=/dev/sdc --runtime=30 --readwrite=randread
>>> --iodepth=1 --random_distribution=zoned:18/90:7/5:75/5 --norandommap
>>> --output-format=terse
>>> histogram bins = [2302, 25, 25, 30, 33, 36, 26, 32, 29, 37, 21, 21,
>>> 32, 27, 49, 34, 24, 36, 26, 184]
>>> histogram percents = [75.99867943215582, 0.8253549026081215,
>>> 0.8253549026081215, 0.9904258831297458, 1.0894684714427203,
>>> 1.188511059755695, 0.8583690987124464, 1.0564542753383954,
>>> 0.9574116870254209, 1.2215252558600198, 0.6932981181908221,
>>> 0.6932981181908221, 1.0564542753383954, 0.8913832948167713,
>>> 1.6176956091119181, 1.1224826675470452, 0.7923407065037966,
>>> 1.188511059755695, 0.8583690987124464, 6.074612083195774]
>>>
>>> Using fio --name=rand_reads --ioengine=libaio --direct=1 --exitall
>>> --thread --filename=/dev/sdc --runtime=30 --readwrite=randread
>>> --iodepth=1 --random_distribu   tion=zoned:75/5:7/5:18/90
>>> --norandommap --output-format=terse
>>> histogram bins = [2306, 25, 25, 30, 33, 36, 26, 32, 29, 37, 21, 21,
>>> 32, 27, 49, 34, 24, 36, 26, 184]
>>> histogram percents = [76.03033300362677, 0.8242664029014177,
>>> 0.8242664029014177, 0.9891196834817013, 1.0880316518298714,
>>> 1.1869436201780414, 0.8572370590174745, 1.0550609957138146,
>>> 0.9561490273656446, 1.2199142762940982, 0.6923837784371909,
>>> 0.6923837784371909, 1.0550609957138146, 0.8902077151335311,
>>> 1.6155621496867787, 1.1210023079459281, 0.7912957467853611,
>>> 1.1869436201780414, 0.8572370590174745, 6.0666007253544345]
>>>
>>> To run the script, use the -h flag to see usage, but at a minimum
>>> you'll need to give the device handle to run on as the first argument
>>> (the workload only does reads). The random_distribution argument is
>>> set at the top of the file.
>>
>> I'll take a look at this tomorrow, that does seem very fishy.
>>
>>> Here is my environment information:
>>> # cat /etc/centos-release
>>> CentOS Linux release 7.3.1611 (Core)
>>> # uname -r
>>> 3.10.0-514.21.1.el7.x86_64
>>> I used fio-3.2-13-g40e5f which was the newest version I could see as of today.
>>>
>>> As for the feature request:
>>> I am trying to adapt our current FIO job files for FLEX testing which
>>> is a new protocol we announced recently
>>> (http://blog.seagate.com/intelligent/new-flex-dynamic-recording-method-redefines-data-center-hard-drive/)
>>> that has some requirements on where writes/reads are allowed. I would
>>> like to have better control where random reads and writes are going
>>> using the zoned random_distribution setting using sector numbers
>>> rather than capacity percentages. Would that be a possible feature to
>>> add? Or is there an existing way to randomly read/write to
>>> non-contiguous zones on the disk with varying sizes?
>>
>> The best way to request something like that is to come up with a logical
>> way to describe it. That's usually the hardest part, implementing it is
>> usually not that hard. This is especially important since it has to be
>> intuitively easy to use for the user, not requiring them to pour too
>> much over man pages.
>>
>> For yours, the zoned setup already supports split ranges for
>> reads/writes/trims. The change seems to be that you want to give the
>> zones in absolute sizes instead. It'd be the easiest to extend the
>> zoning to allow sizes instead.
>>
>> --
>> Jens Axboe
>>


-- 
Jens Axboe