linux-ext4 - Re: [PATCH] Add ext3 data=guarded mode

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Message-ID: <20090419062448.GA13272@amit-x200.pnq.redhat.com>
Date:	Sun, 19 Apr 2009 11:54:48 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Mike Galbraith <efault@....de>
Cc:	Theodore Tso <tytso@....edu>, Chris Mason <chris.mason@...cle.com>,
	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] Add ext3 data=guarded mode

On (Sat) Apr 18 2009 [09:28:21], Mike Galbraith wrote:
> On Sat, 2009-04-18 at 11:33 +0530, Amit Shah wrote:
> > On (Fri) Apr 17 2009 [16:13:42], Theodore Tso wrote:
> > > On Fri, Apr 17, 2009 at 11:39:06PM +0530, Amit Shah wrote:
> > > > # 4GiB file, kernel 9f76208c33984ab777eace5d07a4e36e88703e02 + ext3-guarded
> > > > 
> > > > filesystem	posix-fallocate	mmap	chunk-4096	chunk-8192
> > > > ext3-guarded	85		97	459		90
> > > > ext3-writeback 86		95	140		94
> > > > ext3-ordered	86		96	277		95
> > > > 
> > > > Running the test in single user mode, I get the following results:
> > > > 
> > > > # 4GiB file, kernel 9f76208c33984ab777eace5d07a4e36e88703e02 + ext3-guarded
> > > > 
> > > > filesystem	posix-fallocate	mmap	chunk-4096	chunk-8192
> > > > ext3-guarded	84		86	163		91
> > > > ext3-writeback 84		88	217		91
> > > > ext3-ordered	84		86	226		91
> > > 
> > > 
> > > The difference between guarded and writeback in chunk-4096 looking at
> > > your desktop timings and your single user times is.... surprising. 
> > 
> > Surely. I re-ran the guarded test immediately after that one and got a
> > time of 353s with the desktop. Another run much latergave me a 189s time,
> > so it seems to vary quite a lot. Initially when I was getting high
> > numbers, I thought it could be related to the IO scheduler but looks like
> > it's just some background tasks trying to get cpu or io time. Of course,
> > the whole system becomes sluggish once these tests start.
> > 
> > > In particular, the fact that the guarded time is 3 times longer than
> > > ext3-writeback when the desktop is running, and 20% faster in single
> > > user mode.  Are these results reproducible?  And do you have any
> > > thoughts as to what might be causing them?
> > 
> > I initially thought there was something but I also got lower numbers
> > (189s), so I can't really say what it is even though I call sync before
> > starting the tests.
> 
> Probably because you're swapping heavily, and that is perturbing your

The variance only affects the 4k test; the other times more or less
remain the same.

		Amit
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