Mailinglist Archive: opensuse (1239 mails)

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Re: [opensuse] XFS and openSUSE 12.1
  • From: Roger Oberholtzer <roger@xxxxxx>
  • Date: Mon, 03 Jun 2013 21:07:52 +0200
  • Message-id: <1370286472.5064.18.camel@localhost>
On Mon, 2013-06-03 at 12:52 -0400, Greg Freemyer wrote:
On Mon, Jun 3, 2013 at 1:39 PM, Roger Oberholtzer <roger@xxxxxx> wrote:
On Mon, 2013-06-03 at 09:11 -0400, Greg Freemyer wrote:
O_DIRECT

From the open(2) man page:

"The thing that has always disturbed me about O_DIRECT is that
the whole interface is just stupid, and was probably designed
by a deranged monkey on some serious mind-controlling
substances."--Linus

So of course I will have to try it!

I said it will have a major impact. I didn't say if it would be a
good or bad impact!

In general for streaming i/o loads I think it is a good thing. dd as
an example has an option to use O_DIRECT for the i/o. For a normal
random i/o workload it is probably horrible.

OTOH, database tools will sometimes want to totally control how
caching works, so they use O_DIRECT to get as close to the hard drive
as they can.

I have three JPEG compression methods that I play with: (1) the standard
turbo that comes with openSUSE (used in the systems with the issues
described here), (2) a re-implementation of that based on the Intel
Performance Primitives (IPP) (same API/ABI), (3) another one based on
IPP that deals with the image as an object, via a different API.


#2 is 3-4 times faster than #1, and #3 is 6-8 times faster than #1 on
our gray scale images of road surfaces.

All of these will of course provide data of different sizes as the
compressed images vary in size. I do not relish the thought of
maintaining fixed sized buffers from any of these to manage O_DIRECT
disk I/O.


I think I will try a different file system, and then a different disk
device in the computer.

I am rather surprised by all of this as each disk is written to by only
one thread, and only one file at a time is written. There is not a great
demand on writing. The disk access light turns on periodically, once
every second or so. So it would seem that the data is being written
rather often.

I wonder if there is some other system dynamic I am missing. There is
ample memory, and all buffers are pre-allocated. There are 16 cores, and
when I see the system load, 10 are 99% idle.



--

Yours sincerely,

Roger Oberholtzer

OPQ Systems / Ramböll RST

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696
roger.oberholtzer@xxxxxxxxxx
________________________________________

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden
www.rambollrst.se
s

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