Re: IO scheduler

[David Nellans <david@nellans.org>]

On 10/10/2013 12:08 PM, Brian L. wrote:
> Hi there,
>
> I was wondering if you guys use NOOP IO scheduler when you are running fio?
>
> I use the CFQ IO scheduler but I do put the OS into init 1 and run fio
> process one at a time so that I can get accurate readings.
>
> I was wondering what are people practice and experience in the real world.
>
> Thanks,
> Brian L.

Some flash device drivers specifically (Fusion-io does this) use the 
noop scheduler to reduce latency and variance that can be introduced 
when using other schedulers.  Using the no-op scheduler is a reasonable 
thing to do for all drives to make apples to apples, but if a driver 
specifically overrides it to something else, probably worth sticking 
with their settings.

init 1 is overkill.  In a previous life doing a lot of measuring of 
flash - I found that simply making sure the machine was "idle" you could 
get easily get repeatability within 1% for devices doing several hundred 
thousand IOPS, even those with on-load architectures that were sensitive 
to CPU usage.