You are correct. It is also not co-incidental that one of the main things
being tested with the O_DIRECT patches and doing DMA to/from user space is
Oracle. The O_DIRECT flag as with SGI machines does (or can do depending
on the card) direct DMA to and from user pages. This is precisely what
things like a fault tolerant oracle setup on shared scsi or fc busses happens
to need.
> system interfere with that testing? It would seem to me that you're
> assuming that you folks know more about all possible uses of Linux and
> how to best tune the system for all those uses, than anyone who could
> possibly come along and want to use a Linux system for a particular purpose.
I don't think that is the case - all the VM is tuneable and you can already
accurately measure through the page cache throughput (man hdparm for a
simple tool that includes this). If you want to measure raw disk I/O rates
without OS overhead then you can't do it without the patches for raw I/O
Alan
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