linux-kernel - Re: Tux3 Report: How fast can we fsync?

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Message-ID: <7322d870-e627-4ba4-91b4-bcb38ad8d015@phunq.net>
Date:	Thu, 30 Apr 2015 03:59:08 -0700
From:	Daniel Phillips <daniel@...nq.net>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<tux3@...3.org>, Theodore Ts'o <tytso@....edu>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: Tux3 Report: How fast can we fsync?

On Wednesday, April 29, 2015 8:50:57 PM PDT, Mike Galbraith wrote:
> On Wed, 2015-04-29 at 13:40 -0700, Daniel Phillips wrote:
>>
>> That order of magnitude latency difference is striking. It sounds
>> good, but what does it mean? I see a smaller difference here, maybe
>> because of running under KVM.
>
> That max_latency thing is flush.

Right, it is just the max run time of all operations, including flush
(dbench's name for fsync I think) which would most probably be the longest
running one. I would like to know how we manage to pull that off. Now
that you mention it, I see a factor of two or so latency win here, not
the order of magnitude that you saw. Maybe KVM introduces some fuzz
for me.

I checked whether fsync = sync is the reason, and no. Well, that goes
on the back burner, we will no doubt figure it out in due course.

Regards,

Daniel
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