From: Vojtech Pavlik <vojtech@suse.com>
To: shiva rkreddy <shiva.rkreddy@gmail.com>
Cc: Eric Wheeler <bcache@lists.ewheeler.net>, linux-bcache@vger.kernel.org
Subject: Re: Drop in Iops with fsync when using NVMe as cache
Date: Wed, 22 Feb 2017 10:40:57 +0100 [thread overview]
Message-ID: <20170222094057.GD31967@suse.cz> (raw)
In-Reply-To: <CAPntomBf8c6TFBLM5iBuX=OWmfQ-uGCUiDdJnXEn1+-gS7KJaw@mail.gmail.com>
On Tue, Feb 21, 2017 at 10:48:06AM -0600, shiva rkreddy wrote:
> fio command without fsync:
>
> # fio -filename=/dev/bcache0 -direct=1 -ioengine=libaio -rw=randwrite
> -bs=4k -name=mytest -iodepth=1 -runtime=30 -time_based
>
> iops : 35k
>
> fio command with fsync:
>
> fio -filename=/dev/bcache0 -direct=1 -ioengine=libaio -rw=randwrite
> -bs=4k -name=mytest -iodepth=1 -runtime=30 -time_based -fsync=1
>
> iops: 8.1k
> I'm quite surprised by the drop in iops with fsync turned on. Is this
> expected or am I missing some basic setting?
It's not uncommon that fsync would have a huge performance impact.
Without fsync, most of the data never hits the storage and is only
staying in the system memory.
May I suggest that you try to measure the performance of the same tests
when the filesystem is created on the NVMe device directly, without
using bcache? You're likely to observe a similar pattern.
--
Vojtech Pavlik
Director SUSE Labs
next prev parent reply other threads:[~2017-02-22 9:41 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-21 16:48 Drop in Iops with fsync when using NVMe as cache shiva rkreddy
2017-02-22 9:40 ` Vojtech Pavlik [this message]
2017-02-22 15:47 ` shiva rkreddy
2017-03-01 0:55 ` Eric Wheeler
2017-03-01 3:00 ` shiva rkreddy
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