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From: Le Chaud Lapin on 23 Oct 2009 23:56
On Oct 22, 8:03 am, "Paul Baker [MVP, Windows Desktop Experience]"
<paulrichardba...(a)community.nospam> wrote:
> If it's sequential, consider using FILE_FLAG_SEQUENTIAL_SCAN.
> However, the only way to truly know what the performance is is to measure
> it, as Mihai said. See if any of the above things help. Don't forget to
> reboot between tests and repeat them multiple times to ensure you are
> getting consistent results. I believe SysInternals has a tool that clears
> the system cache, but rebooting is easy and eliminates some other possible
> causes of interference too.

I measured it, and it was the ReadFile calls. Basically all the
instructions between SYSENTER and actual buffer fill. 43,000,000 4-
byte/500-byte/etc. reads are not good.

> If you want to "slam" the entire file into memory, why not use a memory
> mapped file?

I did. :)

Performance is now 9x what it was before, on reads only, but that's
including testing in Release mode instead of Debug mode, double
construction in a C++ class, and some minor optimizations. [I have
"Don't forget to optimized this." comments everywhere in my code!]

There is one catch of course: On writing, the file system must be
predetermined with MMIO, which is not possible in my case, so at some
point I will have to use the user-mode buffer technique anyway.

-Le Chaud Lapin-
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