Re: priocscan vs fcfs

["Emile `iMil' Heitor" <imil%home.imil.net@localhost>]

On Wed, 2 Dec 2015, Michael van Elst wrote:

> fcfs is also the "neutral" queue for drivers stacking on top of
> each other. The queue sorting should really only be done
> at one level.
>
> But raidframe is more complicated because it does its own queuing
> and sorting outside of this schema, in particular when it has to
> read-modify-write stripe sets for small I/O.
>
> That's probably why setting the queues all to fcfs is the best
> for you.

Thanks a lot for this clear analysis Michael.

I can now confirm the results I've witnessed earlier, I've ran a couple of
benchmarks, including bonnie++ and iozone, the latter shows a ratio of x5 in
favor of the fsfc strategy for every type of operation. For those interested,
iozone spreadsheet output is available here (OOo / LibreOffice):

https://home.imil.net/tmp/coruscant-iozone-priocscan.ods
https://home.imil.net/tmp/coruscant-iozone-fsfc.ods

For each subset, first column is the amount of data written (from 64K to 4M)
and first row is the block size.

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Emile `iMil' Heitor * <imil@{home.imil.net,NetBSD.org,gcu.info}>
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