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Re: O_DIRECT support

On 2002.05.10 21:31 Stephen C. Tweedie wrote:

On Thu, May 09, 2002 at 11:55:32AM +0100, Ian Leonard wrote:

> I have checked 2.4.18 and 2.5 kernels and there seems to
> be an interface but no actual implementation.
> It has been suggested that it only works with ext2 but we
> need ext3.

That's right.

But the ext2 is pretty much only a wrapper around a generic_direct_IO
function, so it would be pretty easy to use that same wrapper for
ext3.  It would be tricky to make it work with data=journal mode, but
the other data modes ought to be easy to get going.

I my case this wouldn't matter too much. I am trying to improve the performance of an application that writes video data to the disk. I have mounted the relevant filesystem with various data= options but it doesn't seem to make any difference to my test program (which simply writes a large file to disk and times it).

I am far from familiar with the internals of filing systems. Do you
think this feature is likely to appear in the near future. Also would
it be a 2.4 or a 2.5 thing?

Currently through-put doesn't look too bad but I see that there is a drop
off every 30 seconds. I assumed that this was bdflush and fiddled with
the options but haven't seen an improvement yet.

Thanks for your help. Any words of wisdom appreciated.

Ian Leonard
eMail: ileonard ntlworld com
Phone: +44 (0)1865 765273

Please ignore spelling and punctuation - I did.

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