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SubjectRe: O_DIRECT question
Michael Tokarev wrote:
> After all the explanations, I still don't see anything wrong with the
> interface itself. O_DIRECT isn't "different semantics" - we're still
> writing and reading some data. Yes, O_DIRECT and non-O_DIRECT usages
> somewhat contradicts with each other, but there are other ways to make
> the two happy, instead of introducing alot of stupid, complex, and racy
> code all over.

By the way. I just ran - for fun - a read test of a raid array.

Reading blocks of size 512kbytes, starting at random places on a 400Gb
array, doing 64threads.

O_DIRECT: 336.73 MB/sec.
!O_DIRECT: 146.00 MB/sec.

Quite a... difference here.

Using posix_fadvice() does not improve it.

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