Re: CPUs, threads, and speed

[Andrey Kuzmin <andrey.v.kuzmin@gmail.com>]

On Wed, Jan 15, 2020 at 8:29 PM Gruher, Joseph R
<joseph.r.gruher@intel.com> wrote:
>
> > -----Original Message-----
> > From: fio-owner@vger.kernel.org <fio-owner@vger.kernel.org> On Behalf Of
> > Mauricio Tavares
> > Sent: Wednesday, January 15, 2020 7:51 AM
> > To: fio@vger.kernel.org
> > Subject: CPUs, threads, and speed
> >
> > Let's say I have a config file to preload drive that looks like this (stolen from
> > https://github.com/intel/fiovisualizer/blob/master/Workloads/Precondition/fill
> > _4KRandom_NVMe.ini)
> >
> > [global]
> > name=4k random write 4 ios in the queue in 32 queues
> > filename=/dev/nvme0n1
> > ioengine=libaio
> > direct=1
> > bs=4k
> > rw=randwrite
> > iodepth=4
> > numjobs=32
> > buffered=0
> > size=100%
> > loops=2
> > randrepeat=0
> > norandommap
> > refill_buffers
> >
> > [job1]
> >
> > That is taking a ton of time, like days to go. Is there anything I can do to speed it
> > up?
>
> When you say preload, do you just want to write in the full capacity of the drive?

I believe that preload here means what in SSD world is called drive
preconditioning. It means bringing a fresh drive into steady mode
where it gives you the true performance in production over months of
use rather than the unrealistic fresh drive random write IOPS.

> A sequential workload with larger blocks will be faster,

No, you cannot get the job done by sequential writes since it doesn't
populate FTL translation tables like random writes do.

As to taking a ton, the rule of thumb is to give the SSD 2xcapacity
worth of random writes. At today speeds, that should take just a
couple of hours.

Regards,
Andrey

> like:
>
> [global]
> ioengine=libaio
> thread=1
> direct=1
> bs=128k
> rw=write
> numjobs=1
> iodepth=128
> size=100%
> loops=2
> [job00]
> filename=/dev/nvme0n1
>
> Or if you have a use case where you specifically want to write it in with 4K blocks, you could probably increase your queue depth way beyond 4 and see improvement in performance, and you probably don't want to specify norandommap if you're trying to hit every block on the device.
>
> -Joe