From: Jens Axboe <axboe@kernel.dk>
To: Karen Higgins <karen.higgins@sanmina.com>, fio@vger.kernel.org
Subject: Re: FIO Disk Stats - 0% Utilization
Date: Thu, 07 Aug 2014 12:33:02 -0600 [thread overview]
Message-ID: <53E3C65E.5080002@kernel.dk> (raw)
In-Reply-To: <CAPY19uW8EV58gvZ2184DcuJ8gnSG-iTcbbqgWFOLYaHuicwPDA@mail.gmail.com>
On 08/07/2014 11:08 AM, Karen Higgins wrote:
> I am loading a Ramdisk driver in various block driver modes (RQ, BIO,
> and Multi-Queue[MQ]) to compare IOPS.
>
> When I load the driver in BIO mode and run fio, the Disk Stats shows a
> utilization of 0.0%, which makes me wonder if the disk is being
> accessed. On the other hand, when I load the driver in RQ or MQ mode,
> the Disk Stats show a utilization of 100% (or near 100%). The IOPS
> for BIO mode are greater than the IOPS for MQ mode, which is another
> red flag that the BIO mode IOPS may not be accurate.
>
> I am able to successfully perform read/write/verification tests
> outside of fio in all block driver modes.
>
> My question is how can I get an accurate IOPS performance measurement
> for the driver in BIO mode? Is there a bug in fio, or am I missing
> some parameter?
>
> Also, it seems that IOPS should be higher in general for MQ mode. Are
> there any performance tuning suggestions for MQ?
In bio mode, the driver is bypassing the entire stack. This means that
you miss out on certain things, IO stats being one of them.
Since bio is a raw mode, it's also not unusual for it to be slightly
faster than MQ, depending on what you run. Some of that might be due to
a suboptimal conversion to MQ, I can't really say without seeing the
code. Things like IO/part stats can be a bit costly as well, so just
turning that off in MQ mode may make you run closer to the BIO speed.
--
Jens Axboe
next prev parent reply other threads:[~2014-08-07 18:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-07 17:08 FIO Disk Stats - 0% Utilization Karen Higgins
2014-08-07 18:33 ` Jens Axboe [this message]
2014-08-07 18:56 ` Jens Axboe
2014-08-07 19:31 ` Karen Higgins
2014-08-07 19:25 ` Karen Higgins
2014-08-07 19:27 ` Jens Axboe
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