Mailinglist Archive: opensuse (1239 mails)

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[opensuse] Re: XFS and openSUSE 12.1
Roger Oberholtzer wrote:
On Tue, 2013-06-04 at 11:26 -0700, Linda Walsh wrote:
Any buffers are filled up very quickly when you write 25 MB/Sec. So
something happening after 30 minutes is probably not related to general
buffering.
This is where I think you'll benet most by using O_DIRECT in your
open call and either a 2nd thread to handle I/O, or async I/O

By writing to /dev/null instead of a disk you are avoiding the kernel's
disk-io routines as well as the xfs-io routines. I.e. it could be
either one. That's why trying O_DIRECT can help eliminate the kernel's
I/O buffering routines.

I do not think the kernel is the culprit. I think it is the hard disk
itself. We will be trying some higher performance discs.
----
It sounds like you are seeing the overhead of the buffering
in the kernel.

If you don't like O_DIRECT, you could try giving the kernel
hints with the POSIX calls
I.e. calling
posix_fadvise(tfd, 0, 0, POSIX_FADV_DONTNEED);
on each file descriptor you are writing might
help?

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