[NTLUG:Discuss] Disk I/O timings.

[Steve Baker]

> In the absence of a disk cache, the data is loaded when you first access
> the page, as you describe above.  I don't know if Linux caches pages
> managed by the virtual memory swap system at all, let alone if there's
> an aggressive read-ahead mechanism, although your timing results suggest
> that it does and there is.

Excellent - that's the information I needed. Thanks!
 
> I would think that for a real-time system, you would want much greater
> control over the caching policy to be able to control situations like
> this.  (Of course, the exact policy choice may not be as important as
> knowing which choice you've got and what its performance characteristics
> are.)

Yes - that's true.  However, I hardly ever access a file more than once
so the caching isn't really giving me any benefit - or harming me very
much (except that it confuses my ability to understand what's going on!)

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