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Message-ID: <70c01d1d0808080933x59f07f67r6d2b1a0b1ed3bc44@mail.gmail.com>
Date: Fri, 8 Aug 2008 09:33:06 -0700
From: "Mark Wong" <markwkm@gmail.com>
To: "Mark Mielke" <mark@mark.mielke.cc>
Subject: Re: file system and raid performance
Cc: "Andrej Ricnik-Bay" <andrej.groups@gmail.com>,
	"Scott Marlowe" <scott.marlowe@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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On Thu, Aug 7, 2008 at 3:08 PM, Mark Mielke <mark@mark.mielke.cc> wrote:
> Andrej Ricnik-Bay wrote:
>
> 2008/8/8 Scott Marlowe <scott.marlowe@gmail.com>:
>
>
> noatime turns off the atime write behaviour.  Or did you already know
> that and I missed some weird post where noatime somehow managed to
> slow down performance?
>
>
> Scott, I'm quite aware of what noatime does ... you didn't miss a post, but
> if you look at Mark's graphs on
> http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide
> they pretty much all indicate that (unless I completely misinterpret the
> meaning and purpose of the labels), independent of the file-system,
> using noatime slows read/writes down (on average)
>
> That doesn't make sense - if noatime slows things down, then the analysis is
> probably wrong.
>
> Now, modern Linux distributions default to "relatime" - which will only
> update access time if the access time is currently less than the update time
> or something like this. The effect is that modern Linux distributions do not
> benefit from "noatime" as much as they have in the past. In this case,
> "noatime" vs default would probably be measuring % noise.

Anyone know what to look for in kernel profiles?  There is readprofile
(profile.text) and oprofile (oprofile.kernel and oprofile.user) data
available.  Just click on the results number, then the "raw data" link
for a directory listing of files.  For example, here is one of the
links:

http://osdldbt.sourceforge.net/dl380/3disk/sraid5/ext3-journal/seq-read/fio/profiling/oprofile.kernel

Regards,
Mark