From: Jens Axboe <axboe@kernel.dk>
To: Jeff Furlong <jeff.furlong@wdc.com>,
Michael Green <mishagreen@gmail.com>,
"fio@vger.kernel.org" <fio@vger.kernel.org>
Subject: Re: random_generator=lfsr overhead with more disks?
Date: Wed, 21 Mar 2018 08:34:56 -0600 [thread overview]
Message-ID: <512d2421-2399-07db-9ddf-b6776614bae4@kernel.dk> (raw)
In-Reply-To: <BN3PR0401MB145797FEFD095957854800088FD70@BN3PR0401MB1457.namprd04.prod.outlook.com>
On 3/16/18 12:45 PM, Jeff Furlong wrote:
> A few comments:
>
> -How does the cpu utilization look compared between the lfsr and
> default tausworthe generators? Is the cpu util actually higher on
> lfsr? If it is near saturated on 16 devices, then naturally
> throughput would decrease.
The LFSR generator is constant overhead, and it should not degrade as
more jobs are using it. There's no shared state at all.
If I were to guess, then the identical offsets of the jobs is probably a
likely clue, since that is the only real difference between the two
random generators. Are these 16 volumes all completely separate?
Finally, you are having 8 jobs all accessing the same 16 devices. You'll
likely get more consistent performance if you split things up a bit by
having 4 jobs, each doing IO to just two of the disks. This shouldn't
really be impacted by the random generator, but your current setup is
prone to performance fluctuations.
--
Jens Axboe
next prev parent reply other threads:[~2018-03-21 14:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-13 19:23 random_generator=lfsr overhead with more disks? Michael Green
2018-03-16 18:45 ` Jeff Furlong
2018-03-16 21:16 ` Michael Green
[not found] ` <BN3PR0401MB145715070B7B9F0C71A902318FD70@BN3PR0401MB1457.namprd04.prod.outlook.com>
[not found] ` <902A0A2A-8708-4A94-A09E-5D3C9BFB48FF@gmail.com>
[not found] ` <SN6PR04MB4064D865EBEB79DE2219218D8FD70@SN6PR04MB4064.namprd04.prod.outlook.com>
2018-03-16 22:32 ` Michael Green
2018-03-17 5:42 ` Sitsofe Wheeler
2018-03-29 7:24 ` Michael Green
2018-03-29 8:56 ` Sitsofe Wheeler
2018-03-16 21:16 ` Michael Green
2018-03-21 14:34 ` Jens Axboe [this message]
2018-03-29 7:28 ` Michael Green
2018-03-29 8:50 ` Sitsofe Wheeler
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